Name: the corneal micropocket assay: a model of angiogenesis in the mouse eye
Uploaded: 2014-08-16T17:00:00
Description: Watch this Scientific Journal Video about The Corneal Micropocket Assay: A Model of Angiogenesis in the Mouse Eye at JoVE.com

We thank Kristin Johnson for the graphic work.

All protocols involving animals are presented to and approved by the Institutional Animal Care and Use Committee at Children&#39;s Hospital Boston and are conducted in accordance with the recommendations of the Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC). Be sure to use sterile instrumentation and aseptic techniqure while performing the procedure.&#160;
1. Preparation of Pellets
<ol>
	<li>Weigh out 10 mg of sucralfate and 60 mg of hydron with the sterile un...

<ol>
	<li>Gospodarowicz, D., Moran, J., Braun, D., Birdwell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clonal+growth+of+bovine+vascular+endothelial+cells:+fibroblast+growth+factor+as+a+survival+agent.">Clonal growth of bovine vascular endothelial cells: fibroblast growth factor as a survival agent.</a> Proc. Natl. Acad. Sci. USA. 73, 4120-4124 (1976).</li><li>Glaser, B. M., D'Amore, P. A., Seppa, H., Seppa, S., Schiffmann, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adult+tissues+contain+chemoattractants+for+vascular+endothelial+cells.">Adult tissues contain chemoattractants for vascular endothelial cells.</a> Nature. 288, 483-484 (1980).</li><li>Kubota, Y., Kleinman, H. K., Martin, G. R., Lawley, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+laminin+and+basement+membrane+in+the+morphological+differentiation+of+human+endothelial+cells+into+capillary-like+structures.">Role of laminin and basement membrane in the morphological differentiation of human endothelial cells into capillary-like structures.</a> J. Cell Biol. 107, 1589-1598 (1988).</li><li>Montesano, R., Orci, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor-promoting+phorbol+esters+induce+angiogenesis+in+vitro.">Tumor-promoting phorbol esters induce angiogenesis in vitro.</a> Cell. 42, 469-477 (1985).</li><li>Korff, T., Augustin, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integration+of+endothelial+cells+in+multicellular+spheroids+prevents+apoptosis+and+induces+differentiation.">Integration of endothelial cells in multicellular spheroids prevents apoptosis and induces differentiation.</a> J. Cell Biol. 143, 1341-1352 (1998).</li><li>Nicosia, R. F., Tchao, R., Leighton, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histotypic+angiogenesis+in+vitro:+light+microscopic,+ultrastructural,+and+radioautographic+studies.">Histotypic angiogenesis in vitro: light microscopic, ultrastructural, and radioautographic studies.</a> In Vitro. 18, 538-549 (1982).</li><li>Wong, K. H., Chan, J. M., Kamm, R. D., Tien, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+models+of+vascular+functions.">Microfluidic models of vascular functions.</a> Annu Rev Biomed Eng. 14, 205-230 (2012).</li><li>Sandison, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+method+for+the+microscopic+study+of+living+growing+tissues+by+the+introduction+of+a+transparent+chamber+in+the+rabbit's+ear.">A new method for the microscopic study of living growing tissues by the introduction of a transparent chamber in the rabbit's ear.</a> Anat. Rec. 28, 281-287 (1924).</li><li>Jain, R. K., Schlenger, K., Hockel, M., Yuan, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+angiogenesis+assays:+progress+and+problems.">Quantitative angiogenesis assays: progress and problems.</a> Nat. Med. 3, 1203-1208 (1997).</li><li>Rogers, M. S., Birsner, A. E., D'Amato, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mouse+cornea+micropocket+angiogenesis+assay.">The mouse cornea micropocket angiogenesis assay.</a> Nat. Protoc. 2 (10), 2545-2550 (2007).</li><li>Gimbrone, M. A., Leapman, S. B., Cotran, R. S., Folkman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor+dormancy+in+vivo+by+prevention+of+neovascularization.">Tumor dormancy in vivo by prevention of neovascularization.</a> J. Exp. Med. 136, 261-276 (1972).</li><li>Gimbrone, M. A., Cotran, R. S., Leapman, S. B., Folkman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor+growth+and+neovascularization:+an+experimental+model+using+the+rabbit+cornea.">Tumor growth and neovascularization: an experimental model using the rabbit cornea.</a> J. Natl. Cancer Inst. 52, 413-427 (1974).</li><li>Rohan, R. M., Fernandez, A., Udagawa, T., Yuan, J., D'Amato, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+heterogeneity+of+angiogenesis+in+mice.">Genetic heterogeneity of angiogenesis in mice.</a> FASEB J. 14 (7), 871-876 (2000).</li><li>Chang, L. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dose-dependent+response+of+FGF-2+for+lymphangiogenesis.">Dose-dependent response of FGF-2 for lymphangiogenesis.</a> Proc Natl Acad Sci U S A. 101 (32), 11658-11663 (2004).</li><li>Udagawa, T., Birsner, A. E., Wood, M., D'Amato, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronic+suppression+of+angiogenesis+following+radiation+exposure+is+independent+of+hematopoietic+reconstitution.">Chronic suppression of angiogenesis following radiation exposure is independent of hematopoietic reconstitution.</a> Cancer Res. 67 (5), 2040-2045 (2007).</li><li>Turner, P. V., Albassam, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Susceptibility+of+rats+to+corneal+lesions+after+injectable+anesthesia.">Susceptibility of rats to corneal lesions after injectable anesthesia.</a> Med Comp. 55 (2), 175-182 (2005).</li><li>Calderone, L., Grimes, P., Shalev, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acute+reversible+cataract+induced+by+xylazine+and+by+ketamine-xylazine+anesthesia+in+rats+and+mice.">Acute reversible cataract induced by xylazine and by ketamine-xylazine anesthesia in rats and mice.</a> Exp. Eye Res. 42, 331-337 (1986).</li></ol>

There are several critical steps in performing a successful corneal assay.&#160; The first is making uniform pellets capable of being implanted and stimulating vessels.&#160; The most important parts of pellet preparation are 1) using carrier-free growth factor; 2) ensuring a good mixture of growth factor with the sucralfate and hydron and 3) moving the final mixture swiftly but carefully from the eppendorf tube to the mesh where the pellets are cast.&#160; It is recommended that &#34;dummy&#34; pellets be made without g...

The process of angiogenesis, the formation of new blood vessels form preexisting ones, is highly complex and is regulated by several endogenous factors that control different steps of vessel sprouting and morphogenesis.&#160; Angiogenesis is triggered due to a shift in balance between pro- and anti-angiogenic factors, a balance that normally maintains the vasculature in a quiescent state.&#160; Angiogenesis in adults occurs in certain physiological conditions such as during the female ovarian cycle or in repair processes such as wound healing and tissue regeneration. &#160;However, it is also a hallmark of several pathologies including malignancies, autoimmune conditions and inflammatory diseases. &#160;The involvement of angiogenesis in these physiological and pathological conditions makes it an important subject for research and an attractive target for therapy.
Due to the complexity of angiogenesis and the involvement of several cells and factors in the process, including endothelial cells, pericytes, circulating cells and stromal cells, in vitro models remain limited and cannot recapitulate the unique in vivo microenvironment.&#160; &#160;The main in vitro assays of angiogenesis are largely focused on observing direct effects on endothelial cells and measuring certain steps in angiogenic process under controlled conditions. These assays include the quantification of endothelial cell proliferation1, migration2, network formation3, tube formation4 and sprouting from spheroids5. &#160;Ex vivo models, unlike the in vitro ones, are more complex and incorporate multiple tissue cell types, an example being the aortic ring assay6.&#160; Nevertheless, like other systems, it cannot capture the contribution of circulating cells and the natural stroma of endothelial cells as exists in vivo.&#160; Attempts to study angiogenesis under flow to mimic the in vivo setting are performed using microfluidic systems7, however even these assays, although much improved, are still unable to account for all the compartments existing in vivo.
Due to the limitations of the in vitro and ex vivo angiogenesis models, in vivo models remain the more reliable choices for angiogenesis studies.&#160; Examples of these models include the implantation of transparent chambers, &#34;windows&#34;, that allow the visualization of growing blood vessels under microscope8, injectable subcutaneous implants such as matrigel and vessel formation in normal tissues such as mouse ear and the chicken chorioallantoic membrane (CAM).&#160; However, one of the most acceptable and quantitative in vivo angiogenesis models is the corneal micropocket neovascularization assay described here, which exploits the naturally avascular cornea as a &#34;screen&#34; to visualize and assess new angiogenic growth9.
Here we describe the corneal micropocket assay as developed in mice.&#160; Initially the model was used to measure nonspecific angiogenic stimuli in rabbit corneas. This was done by introducing tumor pieces into the aqueous humor of the anterior chamber of the rabbit eye and measured tumor-induced neovascularization11.
&#160;However, the assay was later evolved to study effects of specific growth factors10 to better specify and standardize the angiogenic effect.&#160;&#160; In order to release the growth factor in the eye, slow-release pellets containing known quantities of angiogenic growth factors were used instead of tissues.&#160; The availability of purified recombinant angiogenic proteins such as bFGF or VEGF enabled their use as specific targets of angiogenesis modulaters12.&#160; Initially, the assay was largely used in rabbits, which are easier to work with due to their size but later the model was translated into mice; a smaller and less expensive animal model.&#160; Shifting from rabbit to mice provided an important advantage of being able to use genetically manipulated animals, thereby creating a new area of research into the genetic components impacting angiogenesis13.&#160; In addition to the more acceptable usage of cornea assay in studying angiogenesis, other biological processes can also being investigated using modified assays.&#160; For example, studies of lymphangiogenesis were made possible through the implantation of low dose bFGF pellets which allowed the visualization of lymphatic vessels through specific molecular markers14.&#160; In addition, this assay has provided a means to evaluate the effects of radiation on angiogenesis15.
In summation, the corneal micropocket angiogenesis assay is a quantitative, reproducible, flexible assessment of angiogenesis in vivo.&#160; A major advantage of this assay is that the measurement of background vessels is unnecessary because the vessels grow on a naturally avascular tissue.&#160; We describe here the protocol of this assay in details and discuss different scenarios which can occur. The assay consists of 3 discrete segments.&#160; Here we will describe the preparation of growth factor-inclusive pellets, the subsequent surgical implantation and finally the method used to quantify the resulting neovascular growth.

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			<td height="21" style="height:21px;width:216px;">Section 1: Pellet preparation</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sucralfate</td>
			<td style="width:111px;">Sigma</td>
			<td style="width:119px;">#S0652</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hydron (aka Poly(2-Hema))</td>
			<td style="width:111px;">Sigma</td>
			<td style="width:119px;">#P3932-10G</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ethanol</td>
			<td style="width:111px;">Pharmco Products Inc</td>
			<td style="width:119px;">#111000200CSGL</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Growth factors:</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td>Must be carrier-free (no bovine serum albumin(BSA))</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">&#160;Fibroblast growth factor (FGF)</td>
			<td style="width:111px;">PeproTech</td>
			<td style="width:119px;">#AF-100-18B</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Vascular endothelial growth factor (VEGF)</td>
			<td style="width:111px;">R &#38; D Systems</td>
			<td style="width:119px;">#293-VE-050/CF</td>
			<td></td>
		</tr>
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			<td height="21" style="height:21px;width:216px;">35 mm dish</td>
			<td style="width:111px;">Becton-Dickson</td>
			<td style="width:119px;">#353001</td>
			<td>Used for storage of pellets</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">10 cm petri dish</td>
			<td style="width:111px;">VWR</td>
			<td style="width:119px;">#25384-342</td>
			<td>Used as work surface for preparing pellets</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Mesh</td>
			<td style="width:111px;">Sefar America</td>
			<td style="width:119px;">#03--300/51</td>
			<td>300 um nitex nylon, cut into cm square pieces and sterilzed in autoclave</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Spatulas</td>
			<td style="width:111px;">Fisher Scientific</td>
			<td style="width:119px;">#21-401-10</td>
			<td>Use tapered end of one to break up pellet mixture. Bend tapered end of other to help remove mixture from microcentrifuge tube.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microcentrifuge tubes</td>
			<td style="width:111px;">Fisher Scientific</td>
			<td style="width:119px;">#05-408-146</td>
			<td>One for hydron, one for sucralfate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Jewelers forceps, #5</td>
			<td style="width:111px;">Ambler Surgical</td>
			<td style="width:119px;">#2315E</td>
			<td>Need 2 for pulling mesh apart</td>
		</tr>
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			<td height="42" style="height:42px;width:216px;">Centrifugal evaporator</td>
			<td style="width:111px;">ThermoSavant</td>
			<td style="width:119px;">DNA110 SpeedVac</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="42" style="height:42px;width:216px;">Section 2: Surgical implantation of pellets</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Operating microscope</td>
			<td style="width:111px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">2.5% Avertin</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td>General anesthetic</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Proparacaine hydrochloride ophthalmic solution 0.5%</td>
			<td style="width:111px;">Falcon</td>
			<td>NDC# 6131401601</td>
			<td>Eye anesthetic</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Triple Antibiotic Ophthalmic Ointment</td>
			<td style="width:111px;">Bausch &#38; Lomb</td>
			<td style="width:119px;">NDC# 2420878055</td>
			<td>Contains neomycin, polymixin and bacitracin</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ophthalmic microknife, 5 mm</td>
			<td style="width:111px;">Surgistar</td>
			<td style="width:119px;">#924501</td>
			<td>30 degree angle</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">von Graef knife</td>
			<td style="width:111px;">Ambler Surgical</td>
			<td style="width:119px;">#3401E</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Jewelers forceps, #1</td>
			<td style="width:111px;">Ambler Surgical</td>
			<td style="width:119px;">#2301E</td>
			<td>Must be blunted with sharpening stone for proptosing eye</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Jewelers forceps, #5</td>
			<td style="width:111px;">Ambler Surgical</td>
			<td style="width:119px;">#2305E</td>
			<td>For picking up pellets and placing on eye</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Small curved scissors</td>
			<td style="width:111px;">Ambler Surgical</td>
			<td style="width:119px;">#5636E</td>
			<td>For trimming whiskers</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Gauze</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td>For blotting eye after proparacaine</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
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			<td height="42" style="height:42px;width:216px;">Section 3: Grading of Corneal Neovascularization</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">2.5% Avertin</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td>General anesthetic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Slit lamp</td>
			<td style="width:111px;">Nikon</td>
			<td style="width:119px;">FS-2</td>
			<td>Needs an ocular with a reticule to assist in measuring</td>
		</tr>
	</tbody>
</table>

the corneal micropocket assay: a model of angiogenesis in the mouse eye

The mouse corneal micropocket assay is a robust and quantitative in vivo assay for evaluating angiogenesis. By using standardized slow-release pellets containing specific growth factors that trigger blood vessel growth throughout the naturally avascular cornea, angiogenesis can be measured and quantified. In this assay the angiogenic response is generated over the course of several days, depending on the type and dose of growth factor used. The induction of neovascularization is commonly triggered by either basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF). By combining these growth factors with sucralfate and hydron (poly-HEMA (poly(2-hydroxyethyl methacrylate))) and casting the mixture into pellets, they can be surgically implanted in the mouse eye. These uniform pellets slowly-release the growth factors over five or six days (bFGF or VEGF respectively) enabling sufficient angiogenic response required for vessel area quantification using a slit lamp. This assay can be used for different applications, including the evaluation of angiogenic modulator drugs or treatments as well as comparison between different genetic backgrounds affecting angiogenesis. A skilled investigator after practicing this assay can implant a pellet in less than 5 min per eye.

Typical results for bFGF and VEGF pellets in the normal low angiogenic C57BL/6J mice are shown in Figure 2A and B, respectively.&#160; Figure 2E shows the normal distribution of vessel area (VA) in the C57BL/6J strain with varying doses of these growth factors.&#160; 80 ng bFGF pellets normally result in a VA of approximately 2.0 mm2, though values in a range of 1.8-2.4 mm2 are acceptable.&#160; 200 ng VEGF pellets typically cause a response of appr...

Watch this Scientific Journal Video about The Corneal Micropocket Assay: A Model of Angiogenesis in the Mouse Eye at JoVE.com

The Corneal Micropocket Assay: A Model of Angiogenesis in the Mouse Eye

The protocol describes the corneal micropocket assay as developed in mice.

The mouse corneal micropocket assay is a robust and quantitative in vivo assay for evaluating angiogenesis. By using standardized slow-release pellets ...

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