Name: porcine corneal tissue explant to study the efficacy of herpes simplex virus-1 antivirals
Uploaded: 2021-09-20T15:00:00
Description: Watch this Scientific Journal Video about Porcine Corneal Tissue Explant to Study the Efficacy of Herpes Simplex Virus-1 Antivirals at JoVE.com

This study was supported by NIH grants (R01 EY024710, RO1 AI139768, and RO1 EY029426) to D.S. A.A. was supported by an F30EY025981 grant from the National Eye Institute, NIH.Study was conducted using the porcine corneas obtained from Park Packing company, 4107 Ashland Avenue, New City, Chicago, IL-60609

All the porcine tissue used in this study was provided by a third-party private organization and none of the animal handling was performed by University of Illinois at Chicago personnel.
1. Materials
<ol>
	<li>Reagents
	<ol>
		<li>Use following reagents for Plaque assay: powder methylcellulose, Dulbecco&#39;s modified eagle&#39;s medium (DMEM), fetal bovine serum (FBS), penicillin and streptomycin (P/S) for Plaque assay.</li>
		<li>Use crystal violet tablets and ethanol (mol...

<ol>
	<li>Liesegang, 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=Herpes+simplex+virus+epidemiology+and+ocular+importance.">Herpes simplex virus epidemiology and ocular importance.</a> Cornea. 20 (1), 1-13 (2001).</li><li>Farooq, A. V., Valyi-Nagy, T., Shukla, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mediators+and+mechanisms+of+herpes+simplex+virus+entry+into+ocular+cells.">Mediators and mechanisms of herpes simplex virus entry into ocular cells.</a> Current Eye Research. 35 (6), 445-450 (2010).</li><li>Farooq, A. V., Shah, A., Shukla, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+herpesviruses+in+ocular+infections.">The role of herpesviruses in ocular infections.</a> Virus Adaptation and Treatment. 2 (1), 115-123 (2010).</li><li>Xu, F., 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=Seroprevalence+and+coinfection+with+herpes+simplex+virus+type+1+and+type+2+in+the+United+States,+1988-1994.">Seroprevalence and coinfection with herpes simplex virus type 1 and type 2 in the United States, 1988-1994.</a> Journal of Infectious Diseases. 185 (8), 1019-1024 (2002).</li><li>Xu, F., 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=Trends+in+herpes+simplex+virus+type+1+and+type+2+seroprevalence+in+the+United+States.">Trends in herpes simplex virus type 1 and type 2 seroprevalence in the United States.</a> Journal of the American Medical Association. 296 (8), 964-973 (2006).</li><li>Koganti, R., Yadavalli, T., Shukla, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+and+emerging+therapies+for+ocular+herpes+simplex+virus+type-1+infections.">Current and emerging therapies for ocular herpes simplex virus type-1 infections.</a> Microorganisms. 7 (10), (2019).</li><li>Lobo, A. -., Agelidis, A. M., Shukla, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pathogenesis+of+herpes+simplex+keratitis:+The+host+cell+response+and+ocular+surface+sequelae+to+infection+and+inflammation.">Pathogenesis of herpes simplex keratitis: The host cell response and ocular surface sequelae to infection and inflammation.</a> Ocular Surface. 17 (1), 40-49 (2019).</li><li>Koujah, L., Suryawanshi, R. K., Shukla, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pathological+processes+activated+by+herpes+simplex+virus-1+(HSV-1)+infection+in+the+cornea.">Pathological processes activated by herpes simplex virus-1 (HSV-1) infection in the cornea.</a> Cellular and Molecular Life Sciences. 76 (3), 405-419 (2019).</li><li>Lass, J. H., 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=Antiviral+medications+and+corneal+wound+healing.">Antiviral medications and corneal wound healing.</a> Antiviral Research. 4 (3), 143-157 (1984).</li><li>Burns, W. H., 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=Isolation+and+characterisation+of+resistant+Herpes+simplex+virus+after+acyclovir+therapy.">Isolation and characterisation of resistant Herpes simplex virus after acyclovir therapy.</a> Lancet. 1 (8269), 421-423 (1982).</li><li>Crumpacker, C. S., 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=Resistance+to+antiviral+drugs+of+herpes+simplex+virus+isolated+from+a+patient+treated+with+Acyclovir.">Resistance to antiviral drugs of herpes simplex virus isolated from a patient treated with Acyclovir.</a> New England Journal of Medicine. 306 (6), 343-346 (2010).</li><li>Yildiz, C., 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=Acute+kidney+injury+due+to+acyclovir.">Acute kidney injury due to acyclovir.</a> CEN Case Report. 2 (1), 38-40 (2013).</li><li>Fleischer, R., Johnson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acyclovir+nephrotoxicity:+a+case+report+highlighting+the+importance+of+prevention,+detection,+and+treatment+of+acyclovir-induced+nephropathy.">Acyclovir nephrotoxicity: a case report highlighting the importance of prevention, detection, and treatment of acyclovir-induced nephropathy.</a> Case Rep Med. 2010, 1-3 (2010).</li><li>Thakkar, N., 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=Cultured+corneas+show+dendritic+spread+and+restrict+herpes+simplex+virus+infection+that+is+not+observed+with+cultured+corneal+cells.">Cultured corneas show dendritic spread and restrict herpes simplex virus infection that is not observed with cultured corneal cells.</a> Science Report. 7, 42559 (2017).</li><li>Pescina, S., 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=et+al+Development+of+a+convenient+ex+vivo+model+for+the+study+of+the+transcorneal+permeation+of+drugs:+Histological+and+permeability+evaluation.">et al Development of a convenient ex vivo model for the study of the transcorneal permeation of drugs: Histological and permeability evaluation.</a> Journal of Pharmaceutical Sciences. 104, 63-71 (2015).</li><li>Jaishankar, D., 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=An+off-target+effect+of+BX795+blocks+herpes+simplex+virus+type+1+infection+of+the+eye.">An off-target effect of BX795 blocks herpes simplex virus type 1 infection of the eye.</a> Science Translational Medicine. 10, 5861 (2018).</li><li>Duggal, N., 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=Zinc+oxide+tetrapods+inhibit+herpes+simplex+virus+infection+of+cultured+corneas.">Zinc oxide tetrapods inhibit herpes simplex virus infection of cultured corneas.</a> Molecular Vision. 23, 26-38 (2017).</li></ol>

Prior research has shown BX795 to have a promising role as an antiviral agent against HSV-1 infection; by inhibiting the TANK-binding kinase 1 (TBK1)16. Both TBK1 and autophagy have played a role in helping inhibit HSV-1 infection as demonstrated on human corneal epithelial cells. BX795 was shown to be maximally effective with antiviral activity at a concentration of 10&#181;M and using both western blot analysis and viral plaque analysis of key viral proteins, BX795 was shown to inhibit HSV-1 inf...

People suffering from ocular infections often incur vision loss1. With a high seroprevalence worldwide, HSV infected individuals suffer from recurring eye infections which lead to corneal scarring, stromal keratitis and neovascularization2,3,4,5. HSV infections have also shown to cause less frequently, a range of serious conditions among immunocompromised, untreated patients like encephalitis and systemic morbidity6,7,8. Drugs like Acyclovir (ACV) and its nucleoside analogs have shown consistent success in curbing HSV-1 infection and even control reactivation yet the prolonged use of these drugs is associated with renal failure, fetal abnormalities and failure to restrict the emergence of drug-resistance to evolving viral strains9,10,11,12,13. Complexities associated with HSV-1 ocular infections, have been previously studied in vitro using monolayers and 3D cultures of human corneal cells and in vivo using murine or rabbit ocular infections. While these in vitro models provide significant data on the cellular biological components of HSV-1 infections, they, however, fail to mimic the intricate complexity of corneal tissue and do little to illuminate the dendritic spread of the virus14. In contrast, although in vivo systems are more insightful in showing infection spread in corneas and immune activation responses during HSV-1 infection, they do come with the caveat that they require trained investigators and large facilities for animal care to overlook the experiments.
Here we use porcine corneas as an ex vivo model to examine the HSV-1 infection induced wound system. Both the potential pharmacology of certain drugs as well as the cell and molecular biology of the wound system caused by the infection can be studied through tissue explant cultures. This model may also be amended for the use for other viral and bacterial infections as well. In this study, porcine corneas were used to test the antiviral efficacy of a preclinical small molecule, BX795. The use of porcine corneas was preferred due to ease of access and cost effectiveness. Additionally, porcine corneal models are good models of human eyes with the corneas being easy to isolate, adequately sized for infection and visualization and robust to handle15. Porcine corneas are also comparable to the complexity of human corneal models in both trans corneal permeability and systemic absorption15. By using this model for the study, we were able to elucidate how BX795 is worthy of further investigation as a competent inhibitor of HSV-1 virus infection and adds to the literature of classifying it as a potential small-molecule antiviral compound16.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>30 G hypodermic needles.</td>
			<td>BD</td>
			<td>305128</td>
			<td></td>
		</tr>
		<tr>
			<td>500 mL glass bottle.</td>
			<td>Thomas Scientific</td>
			<td>844027</td>
			<td></td>
		</tr>
		<tr>
			<td>Antimycotic and Antibiotic (AA)</td>
			<td>GIBCO</td>
			<td>15240096</td>
			<td>Aliquot into 5 mL tubes and keep frozen until use</td>
		</tr>
		<tr>
			<td>Benchtop vortexer.</td>
			<td>BioDot</td>
			<td>BDVM-3200</td>
			<td></td>
		</tr>
		<tr>
			<td>Biosafety cabinet with a Bio-Safety Level-2 (BSL-2) certification.</td>
			<td>Thermofisher Scientific</td>
			<td>Herasafe 2030i</td>
			<td></td>
		</tr>
		<tr>
			<td>Calgiswab 6&#34; Sterile Calcium Alginate Standard Swabs.</td>
			<td>Puritan</td>
			<td>22029501</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell scraper - 25 cm</td>
			<td>Biologix BE</td>
			<td>70-1180 70-1250</td>
			<td></td>
		</tr>
		<tr>
			<td>Crystal violet</td>
			<td>Sigma Aldrich</td>
			<td>C6158</td>
			<td>Store the powder in a dark place</td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s modified Eagle&#8217;s medium - DMEM</td>
			<td>GIBCO</td>
			<td>41966029</td>
			<td>Store at 4 &#176;C until use</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma Aldrich</td>
			<td>E7023</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum -FBS</td>
			<td>Sigma Aldrich</td>
			<td>F2442</td>
			<td>Aliquot into 50 mL tubes and keep frozen until use</td>
		</tr>
		<tr>
			<td>Flat edged tweezers &#8211; 2.</td>
			<td>Harward Instruments</td>
			<td>72-8595</td>
			<td></td>
		</tr>
		<tr>
			<td>Freezers --80 &#176;C. -</td>
			<td>Thermofisher Scientific</td>
			<td>13 100 790</td>
			<td></td>
		</tr>
		<tr>
			<td>Fresh box of blades.</td>
			<td>Thomas Scientific</td>
			<td>TE05091</td>
			<td></td>
		</tr>
		<tr>
			<td>Guaze</td>
			<td>Johnson &#38; Johnson</td>
			<td></td>
			<td>108 square inch folder 12 ply</td>
		</tr>
		<tr>
			<td>HSV-1 17GFP</td>
			<td>grown in house</td>
			<td>-</td>
			<td>Original strain from Dr. Patricia Spears, Northwestern University. GFP expressing HSV-1 strain 17</td>
		</tr>
		<tr>
			<td>Insulin, Transferrin, Selenium - ITS</td>
			<td>GIBCO</td>
			<td>41400045</td>
			<td>Aliquot into 5 mL tubes and keep frozen until use</td>
		</tr>
		<tr>
			<td>Magnetic stirrer.</td>
			<td>Thomas Scientific</td>
			<td>H3710-HS</td>
			<td></td>
		</tr>
		<tr>
			<td>Metallic Scissors.</td>
			<td>Harward Instruments</td>
			<td>72-8400</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipettes 1 to 1000 &#181;L.</td>
			<td>Thomas Scientific</td>
			<td>1159M37</td>
			<td></td>
		</tr>
		<tr>
			<td>Minimum Essential Medium - MEM</td>
			<td>GIBCO</td>
			<td>11095080</td>
			<td>Store at 4 &#176;C until use</td>
		</tr>
		<tr>
			<td>OptiMEM&#160;</td>
			<td>GIBCO</td>
			<td>31985047</td>
			<td>Store at 4 &#176;C until use</td>
		</tr>
		<tr>
			<td>Penicillin/streptomycin.</td>
			<td>GIBCO</td>
			<td>15140148</td>
			<td>Aliquot into 5 mL tubes and keep frozen until use</td>
		</tr>
		<tr>
			<td>Phosphate Buffer Saline -PBS</td>
			<td>GIBCO</td>
			<td>10010072</td>
			<td>Store at room temperature</td>
		</tr>
		<tr>
			<td>Porcine Corneas</td>
			<td>Park Packaging Co., Chicago, IL</td>
			<td>0</td>
			<td>Special order by request</td>
		</tr>
		<tr>
			<td>Procedure bench covers - as needed.</td>
			<td>Thermofisher Scientific</td>
			<td>S42400</td>
			<td></td>
		</tr>
		<tr>
			<td>Serological Pipettes</td>
			<td>Thomas Scientific</td>
			<td>P7132, P7127, P7128, P7129, P7137</td>
			<td></td>
		</tr>
		<tr>
			<td>Serological Pipetting equipment.</td>
			<td>Thomas Scientific</td>
			<td>Ezpette Pro</td>
			<td></td>
		</tr>
		<tr>
			<td>Stereoscope</td>
			<td>Carl Zeiss</td>
			<td>SteREO Discovery V20</td>
			<td></td>
		</tr>
		<tr>
			<td>Stirring magnet.</td>
			<td>Thomas Scientific</td>
			<td>F37120</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue culture flasks, T175 cm2.</td>
			<td>Thomas Scientific</td>
			<td>T1275</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue culture incubators which can maintain 5% CO2 and 37 &#176;C temperature.</td>
			<td>Thermofisher Scientific</td>
			<td>Forma 50145523</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue culture treated plates (6-well).</td>
			<td>Thomas Scientific</td>
			<td>T1006</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA (0.05%), phenol red</td>
			<td>GIBCO</td>
			<td>25-300-062</td>
			<td>Aliquot into 10 mL tubes and keep frozen until use</td>
		</tr>
		<tr>
			<td>Vero cells</td>
			<td>American Type Culture Collection ATCC</td>
			<td>CRL-1586</td>
			<td></td>
		</tr>
	</tbody>
</table>

porcine corneal tissue explant to study the efficacy of herpes simplex virus-1 antivirals

Viruses and bacteria can cause a variety of ocular surface defects and degeneration such as wounds and ulcers through corneal infection. With a seroprevalence that ranges from 60-90% worldwide, the Herpes Simplex Virus type-1 (HSV-1) commonly causes mucocutaneous lesions of the orofacial region which also manifest as lesions and infection-associated blindness. While current antiviral drugs are effective, emergence of resistance and persistence of toxic side-effects necessitates development of novel antivirals against this ubiquitous pathogen. Although in vitro assessment provides some functional data regarding an emerging antiviral, they do not demonstrate the complexity of ocular tissue in vivo. However, in vivo studies are expensive and require trained personnel, especially when working with viral agents. Hence ex vivo models are efficient yet inexpensive steps for antiviral testing. Here we discuss a protocol to study infection by HSV-1 using porcine corneas ex vivo and a method to treat them topically using existing and novel antiviral drugs. We also demonstrate the method to perform a plaque assay using HSV-1. The methods detailed may be used to conduct similar experiments to study infections that resemble the HSV-1 pathogen.

To understand the efficacy of the experimental antivirals, they need to be tested extensively before they are sent for in vivo human clinical trials. In this regard, positive control, negative control and test groups have to be identified. Trifluorothymidine (TFT) has long been used as the preferred treatment to treat herpes keratitis topically16. Used as a positive control, the TFT treated corneal groups show lower infection spread. As a negative control, we used DMSO or vehicle control dissolved...

Watch this Scientific Journal Video about Porcine Corneal Tissue Explant to Study the Efficacy of Herpes Simplex Virus-1 Antivirals at JoVE.com

Porcine Corneal Tissue Explant to Study the Efficacy of Herpes Simplex Virus-1 Antivirals

We describe the use of a porcine cornea to test the antiviral efficacy of experimental drugs.

Viruses and bacteria can cause a variety of ocular surface defects and degeneration such as wounds and ulcers through corneal infection. With a ...

Understanding the efficacy of drugs in animal models is cost and labor intensive. Our protocol which uses an ex vivo tissue explant model is significantly lower both in terms of cost and scientific personnel required to conduct the study. The main advantage of this technique is the use of porcine eyes, which have anatomy and physiology very similar to human eyes as opposed to some other small animal models.When we test drugs in vitro, they might show efficacy which might be absent in animal or human models. Ex vivo tissue systems are the best way to understand whether or not our in vitro systems can be translated into animal and human trials. The porcine cornea system, although less labor intensive, requires trainable skills to isolate, maintain, infect and treat with the drugs, especially the process of isolation of cornea from the entire porcine eye is tricky to express in words, but requires visual demonstration.Upon receiving porcine eyes from a suitable vendor, store the tissues on ice until processing and put on the appropriate personal protection equipment. Disinfect the work area with 70%ethanol and secure a bench cover onto the workspace. When the work area is ready, place the eyes onto a 50 millimeter piece of gauze and use the gauze to grasp the posterior section with one hand.Using a 30 gauge needle, carefully make a single puncture at approximately the center of the epithelial surface of the eye, taking care not to damage the stroma, and use a sharp sterilized blade to make a small incision on the sclera at a one millimeter distance from the cornea. Using a swift and smooth rotating action of the hand and taking care that the vitreous humor does not leak, cut the edge of the cornea and holding the cornea at the cornea-sclera edge with a flat tweezer, use the blade to cut off the remaining tethering membranes. As each cornea is isolated, place the tissues face up into individual wells of a 12-well plate containing two milliliters of cornea medium per well and add five microliters of a five times 10 to the fifth plaque-forming unit of 17 GFP virus solution to the debrided site on each corneal surface.When all of the corneas have been collected, place the plate into at 37 degree Celsius, 5%carbon dioxide incubator for 72 hours and spray any additional eyes not used in the experiment with 10%bleach for their secure disposal in biohazard bags. Every day before the addition of drugs, place the plate of corneas under a stereo microscope and select the GFP filter and a 500 microsecond exposure time. Capture the images at the lowest magnification before imaging the corneas at a series of increasing magnifications until all of the viral spread and dendrite formation can be visualized clearly.When all of the corneas have been imaged, return the plate to the tissue culture incubator. The day before the infection, wash a confluent vero cell culture two times with 10 milliliters of PBS per wash, and treat the cells with one milliliter of 0.05%trypsin per well for five to 10 minutes at 37 degrees Celsius. When the cells have detached, use nine milliliters of whole medium to ensure that the cells dislodge completely from the flask surface and transfer the resulting cell suspension to a 15 milliliter centrifuge tube.Add 300 microliters of cells to each well of a new six well-plate, followed by the addition of two milliliters of medium to each well, then place the plate in the cell culture incubator overnight. The next morning, to collect the virus from each cornea for quantification, soak sterile cotton swab tips in 500 microliters of serum-free medium per swab in multiple microcentrifuge tubes in a biosafety cabinet for at least five minutes. At the end of the incubation, carefully place the infected porcine cornea cultures into the cabinet.Using the wet cotton swabs, make three revolutions clockwise and three revolutions anti-clockwise five millimeters from the center of each infected porcine cornea without applying excessive pressure. At the end of the series of revolutions, rotate each swab in its serum-free medium filled microcentrifuge tube clockwise and anticlockwise five times before cutting the swabs so that the tips fit within each tube with the lid closed. When all of the corneas have been swabbed, vortex the tubes at high speed for one minute.To quantify the amount of virus collected from each cornea, prepare a log10 one-fold dilution of the virus in serum-free medium in microcentrifuge tubes until a dilution of one times 10 to the negative eight is reached. After aspirating the growth medium from each well of cells, transfer one milliliter of each virus dilution starting at one times 10 to the negative three to the plated cell monolayers and place the infected cells in the cell culture incubator for two hours. At the end of the incubation, gently wash each well two times with PBS before adding two milliliters of methylcellulose-laden medium to each well for a 72-hour incubation or until the formation of plaques can be observed.Upon plaque observation, slowly add one milliliter of methanol to the corner of each well for a 15-minute incubation at room temperature. At the end of the incubation, slowly aspirate the contents from each well without disturbing the cell monolayer. Next, label each well with one milliliter of crystal violet working solution, taking care that all of the cells are covered for a 30-minute incubation protected from light.At the end of the incubation, discard the solution and dry the wells on a sheet of absorbent paper, then count the number of plaques at the highest dilution well to quantify the total virus content in the starting solution three times. As observed in this stereoscopic fluorescence imaging analysis, the antiviral efficacy of BX795 is similar to that of TFT in controlling viral spread, while corneas treated with vehicle only demonstrate spread of the virus from the central infection zone to the periphery by six days post-initial viral inoculation. Similarly, the ocular swabs taken on days two and four post-infection exhibit a complete inhibition of virus in the positive control and BX795-treated samples, while a sharp increase in infectious virus titer is observed in the negative control samples.The isolation of the porcine cornea from the whole porcine eye is the most important step. Steps 2.3 to 2.6 are the most crucial in this process. Our model can be used to understand the dendritic spread of the virus in porcine corneas.This method can be extended towards bacterial and fungal infections as well. This method has helped in visualizing dendritic spread of the virus in corneas outside a human model. This model is helpful in testing the efficacy of drugs prior to moving towards animal and human trials.

porcine-corneal-tissue-explant-to-study-efficacy-herpes-simplex-virus

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Immunology and Infection

Using Reverse Genetics to Manipulate the NSs Gene of the Rift Valley Fever Virus MP-12 Strain to Improve Vaccine Safety and Efficacy

Rift Valley fever virus (RVFV), which causes hemorrhagic fever, neurological disorders or blindness in humans, and a high rate abortion and fetal malformation in ruminants1, has been classified as a HHS/USDA overlap select agent and a risk group 3 pathogen. It belongs to the genus Phlebovirus in the family Bunyaviridae and is one of the most virulent members of this family. Several reverse genetics systems for the RVFV MP-12 vaccine strain2,3 as well as wild-type RVFV strains 4-6, including ZH548 and ZH501, have been developed since 2006. The MP-12 strain (which is a risk group 2 pathogen and a non-select agent) is highly attenuated by several mutations in its M- and L-segments, but still carries virulent S-segment RNA3, which encodes a functional virulence factor, NSs. The rMP12-C13type (C13type) carrying 69% in-frame deletion of NSs ORF lacks all the known NSs functions, while it replicates as efficient as does MP-12 in VeroE6 cells lacking type-I IFN. NSs induces a shut-off of host transcription including interferon (IFN)-beta mRNA7,8 and promotes degradation of double-stranded RNA-dependent protein kinase (PKR) at the post-translational level.9,10 IFN-beta is transcriptionally upregulated by interferon regulatory factor 3 (IRF-3), NF-kB and activator protein-1 (AP-1), and the binding of IFN-beta to IFN-alpha/beta receptor (IFNAR) stimulates the transcription of IFN-alpha genes or other interferon stimulated genes (ISGs)11, which induces host antiviral activities, whereas host transcription suppression including IFN-beta gene by NSs prevents the gene upregulations of those ISGs in response to viral replication although IRF-3, NF-kB and activator protein-1 (AP-1) can be activated by RVFV7. . Thus, NSs is an excellent target to further attenuate MP-12, and to enhance host innate immune responses by abolishing the IFN-beta suppression function. Here, we describe a protocol for generating a recombinant MP-12 encoding mutated NSs, and provide an example of a screening method to identify NSs mutants lacking the function to suppress IFN-beta mRNA synthesis. In addition to its essential role in innate immunity, type-I IFN is important for the maturation of dendritic cells and the induction of an adaptive immune response12-14. Thus, NSs mutants inducing type-I IFN are further attenuated, but at the same time are more efficient at stimulating host immune responses than wild-type MP-12, which makes them ideal candidates for vaccination approaches.

The reverse genetics system for the Rift Valley fever virus MP-12 vaccine strain is a useful tool for creating additional MP-12 mutants with increased attenuation and immunogenicity. We describe the protocol to generate and characterize NSs mutant strains.

Rift Valley fever virus (RVFV), which causes hemorrhagic fever, neurological disorders or blindness in humans, and a high rate abortion and fetal ...

A Primary Neuron Culture System for the Study of Herpes Simplex Virus Latency and Reactivation

Herpes simplex virus type-1 (HSV-1) establishes a life-long latent infection in peripheral neurons. This latent reservoir is the source of recurrent reactivation events that ensure transmission and contribute to clinical disease. Current antivirals do not impact the latent reservoir and there are no vaccines. While the molecular details of lytic replication are well-characterized, mechanisms controlling latency in neurons remain elusive. Our present understanding of latency is derived from in vivo studies using small animal models, which have been indispensable for defining viral gene requirements and the role of immune responses. However, it is impossible to distinguish specific effects on the virus-neuron relationship from more general consequences of infection mediated by immune or non-neuronal support cells in live animals. In addition, animal experimentation is costly, time-consuming, and limited in terms of available options for manipulating host processes. To overcome these limitations, a neuron-only system is desperately needed that reproduces the in vivo characteristics of latency and reactivation but offers the benefits of tissue culture in terms of homogeneity and accessibility.
Here we present an in vitro model utilizing cultured primary sympathetic neurons from rat superior cervical ganglia (SCG) (Figure 1) to study HSV-1 latency and reactivation that fits most if not all of the desired criteria. After eliminating non-neuronal cells, near-homogeneous TrkA+ neuron cultures are infected with HSV-1 in the presence of acyclovir (ACV) to suppress lytic replication. Following ACV removal, non-productive HSV-1 infections that faithfully exhibit accepted hallmarks of latency are efficiently established. Notably, lytic mRNAs, proteins, and infectious virus become undetectable, even in the absence of selection, but latency-associated transcript (LAT) expression persists in neuronal nuclei. Viral genomes are maintained at an average copy number of 25 per neuron and can be induced to productively replicate by interfering with PI3-Kinase / Akt signaling or the simple withdrawal of nerve growth factor1. A recombinant HSV-1 encoding EGFP fused to the viral lytic protein Us11 provides a functional, real-time marker for replication resulting from reactivation that is readily quantified. In addition to chemical treatments, genetic methodologies such as RNA-interference or gene delivery via lentiviral vectors can be successfully applied to the system permitting mechanistic studies that are very difficult, if not impossible, in animals. In summary, the SCG-based HSV-1 latency / reactivation system provides a powerful, necessary tool to unravel the molecular mechanisms controlling HSV1 latency and reactivation in neurons, a long standing puzzle in virology whose solution may offer fresh insights into developing new therapies that target the latent herpesvirus reservoir.

The protocol describes an efficient and reproducible model system to study herpes simplex virus type 1 (HSV-1) latency and reactivation. The assay employs homogenous sympathetic neuron cultures and allows for the molecular dissection of virus-neuron interactions using a variety of tools including RNA interference and expression of recombinant proteins.

Herpes simplex virus type-1 (HSV-1) establishes a life-long latent infection in peripheral neurons. This latent reservoir is the source of recurrent ...

Use of Artificial Sputum Medium to Test Antibiotic Efficacy Against Pseudomonas aeruginosa in Conditions More Relevant to the Cystic Fibrosis Lung

There is growing concern about the relevance of in vitro antimicrobial susceptibility tests when applied to isolates of P. aeruginosa from cystic fibrosis (CF) patients. Existing methods rely on single or a few isolates grown aerobically and planktonically. Predetermined cut-offs are used to define whether the bacteria are sensitive or resistant to any given antibiotic1. However, during chronic lung infections in CF, P. aeruginosa populations exist in biofilms and there is evidence that the environment is largely microaerophilic2. The stark difference in conditions between bacteria in the lung and those during diagnostic testing has called into question the reliability and even relevance of these tests3.
 Artificial sputum medium (ASM) is a culture medium containing the components of CF patient sputum, including amino acids, mucin and free DNA. P. aeruginosa growth in ASM mimics growth during CF infections, with the formation of self-aggregating biofilm structures and population divergence4,5,6. The aim of this study was to develop a microtitre-plate assay to study antimicrobial susceptibility of P. aeruginosa based on growth in ASM, which is applicable to both microaerophilic and aerobic conditions.
 An ASM assay was developed in a microtitre plate format. P. aeruginosa biofilms were allowed to develop for 3 days prior to incubation with antimicrobial agents at different concentrations for 24 hours. After biofilm disruption, cell viability was measured by staining with resazurin. This assay was used to ascertain the sessile cell minimum inhibitory concentration (SMIC) of tobramycin for 15 different P. aeruginosa isolates under aerobic and microaerophilic conditions and SMIC values were compared to those obtained with standard broth growth. Whilst there was some evidence for increased MIC values for isolates grown in ASM when compared to their planktonic counterparts, the biggest differences were found with bacteria tested in microaerophilic conditions, which showed a much increased resistance up to a &gt;128 fold, towards tobramycin in the ASM system when compared to assays carried out in aerobic conditions.
 The lack of association between current susceptibility testing methods and clinical outcome has questioned the validity of current methods3. Several in vitro models have been used previously to study P. aeruginosa biofilms7, 8. However, these methods rely on surface attached biofilms, whereas the ASM biofilms resemble those observed in the CF lung9 . In addition, reduced oxygen concentration in the mucus has been shown to alter the behavior of P. aeruginosa2 and affect antibiotic susceptibility10. Therefore using ASM under microaerophilic conditions may provide a more realistic environment in which to study antimicrobial susceptibility.

Use of Artificial Sputum Medium to Test Antibiotic Efficacy Against Pseudomonas aeruginosa in Conditions More Relevant to the Cystic Fibrosis Lung

Current diagnostic antimicrobial susceptibility testing relies on the planktonic growth of isolates in nutrient rich, aerobic conditions. Here, we employ an alternative artificial sputum medium to study antimicrobial susceptibility of Pseudomonas aeruginosa biofilms under both aerobic and microaerophilic conditions more representative of the cystic fibrosis lung.

There  is growing concern about the relevance of in vitro antimicrobial  susceptibility tests when applied to isolates of P. aeruginosa from  cystic ...

Assays for the Identification of Novel Antivirals against Bluetongue Virus

To identify potential antivirals against BTV, we have developed, optimized and validated three assays presented here. The CPE-based assay was the first assay developed to evaluate whether a compound showed any antiviral efficacy and have been used to screen large compound library. Meanwhile, cytotoxicity of antivirals could also be evaluated using the CPE-based assay. The dose-response assay was designed to determine the range of efficacy for the selected antiviral, i.e. 50% inhibitory concentration (IC50) or effective concentration (EC50), as well as its range of cytotoxicity (CC50). The ToA assay was employed for the initial MoA study to determine the underlying mechanism of the novel antivirals during BTV viral lifecycle or the possible effect on host cellular machinery. These assays are vital for the evaluation of antiviral efficacy in cell culture system, and have been used for our recent researches leading to the identification of a number of novel antivirals against BTV.

Three assays, including the cytopathic effect (CPE)-based assay, dose-response assay and Time-of-Addition (ToA) assay have been developed, optimized, validated and utilized to identify novel antivirals against Bluetongue virus (BTV), as well as to determine the possible Mechanism-of-Action (MoA) for newly identified antivirals.

To identify potential antivirals against BTV, we have  developed, optimized and validated three assays presented here. The CPE-based  assay was the first ...

Ex Vivo Infection of Murine Epidermis with Herpes Simplex Virus Type 1

To enter its human host, herpes simplex virus type 1 (HSV-1) must overcome the barrier of mucosal surfaces, skin, or cornea. HSV-1 targets keratinocytes during initial entry and establishes a primary infection in the epithelium, which is followed by latent infection of neurons. After reactivation, viruses can become evident at mucocutaneous sites that appear as skin vesicles or mucosal ulcers. How HSV-1 invades skin or mucosa and reaches its receptors is poorly understood. To investigate the invasion route of HSV-1 into epidermal tissue at the cellular level, we established an ex vivo infection model of murine epidermis, which represents the site of primary and recurrent infection in skin. The assay includes the preparation of murine skin. The epidermis is separated from the dermis by dispase II treatment. After floating the epidermal sheets on virus-containing medium, the tissue is fixed and infection can be visualized at various times postinfection by staining infected cells with an antibody against the HSV-1 immediate early protein ICP0. ICP0-expressing cells can be observed in the basal keratinocyte layer already at 1.5 hr postinfection. With longer infection times, infected cells are detected in suprabasal layers, indicating that infection is not restricted to the basal keratinocytes, but the virus spreads to other layers in the tissue. Using epidermal sheets of various mouse models, the infection protocol allows determining the involvement of cellular components that contribute to HSV-1 invasion into tissue. In addition, the assay is suitable to test inhibitors in tissue that interfere with the initial entry steps, cell-to-cell spread and virus production. Here, we describe the ex vivo infection protocol in detail and present our results using nectin-1- or HVEM-deficient mice.

Ex Vivo Infection of Murine Epidermis with Herpes Simplex Virus Type 1

The skin is one target tissue of the human pathogen herpes simplex virus type 1 (HSV-1). To explore the invasion route of HSV-1 into tissue, we established an ex vivo infection model of murine epidermal sheets which represent the outermost layer of skin.

To enter its human host, herpes simplex virus type 1 (HSV-1) must overcome the barrier of mucosal surfaces, skin, or cornea. HSV-1 targets keratinocytes ...

Fluorescence-based Neuraminidase Inhibition Assay to Assess the Susceptibility of Influenza Viruses to The Neuraminidase Inhibitor Class of Antivirals

The neuraminidase (NA) inhibitors are the only class of antivirals approved for the treatment and prophylaxis of influenza that are effective against currently circulating strains. In addition to their use in treating seasonal influenza, the NA inhibitors have been stockpiled by a number of countries for use in the event of a pandemic. It is therefore important to monitor the susceptibility of circulating influenza viruses to this class of antivirals. There are different types of assays that can be used to assess the susceptibility of influenza viruses to the NA inhibitors, but the enzyme inhibition assays using either a fluorescent substrate or a chemiluminescent substrate are the most widely used and recommended. This protocol describes the use of a fluorescence-based assay to assess influenza virus susceptibility to NA inhibitors. The assay is based on the NA enzyme cleaving the 2&#8242;-(4-Methylumbelliferyl)-&#945;-D-N-acetylneuraminic acid (MUNANA) substrate to release the fluorescent product 4-methylumbelliferone (4-MU). Therefore, the inhibitory effect of an NA inhibitor on the influenza virus NA is determined based on the concentration of the NA inhibitor that is required to reduce 50% of the NA activity, given as an IC50 value.

We describe the use of a phenotypic fluorescence-based neuraminidase inhibition assay to assess the susceptibility of influenza A and B viruses to the neuraminidase inhibitor class of antivirals.

The neuraminidase (NA) inhibitors are the only class of antivirals approved for the treatment and prophylaxis of influenza that are effective against ...

A Method to Test the Efficacy of Handwashing for the Removal of Emerging Infectious Pathogens

Handwashing is widely recommended to prevent infectious disease transmission. However, little comparable evidence exists on the efficacy of handwashing methods in general. Additionally, little evidence exists comparing handwashing methods to determine which are most efficacious at removing infectious pathogens. Research is needed to provide evidence for the different approaches to handwashing that may be employed during infectious disease outbreaks. Here, a laboratory method to assess the efficacy of handwashing methods at removing microorganisms from hands and their persistence in rinse water is described. Volunteers' hands are first spiked with the test organism and then washed with each handwashing method of interest. Generally, surrogate microorganisms are used to protect human subjects from disease. The number of organisms remaining on volunteers' hands after washing is tested using a modified "glove juice" method: the hands are placed in gloves with an eluent and are scrubbed to suspend the microorganisms and make them available for analysis by membrane filtration (bacteria) or plaque assay (viruses/bacteriophages). Rinse water produced from the handwashing is directly collected for analysis. Handwashing efficacy is quantified by comparing the log reduction value between samples taken after handwashing to samples with no handwashing. Rinse water persistence is quantified by comparing rinse water samples from various handwashing methods to samples collected after handwashing with just water. While this method is limited by the need to use surrogate organisms to preserve the safety of human volunteers, it captures aspects of handwashing that are difficult to replicate in an in vitro study and fills research gaps on handwashing efficacy and the persistence of infectious organisms in rinse water.

Handwashing is widely recommended to prevent infectious disease transmission. However, there is little evidence on which handwashing methods are most efficacious at removing infectious disease pathogens. We developed a method to assess the efficacy of handwashing methods at removing microorganisms.

Handwashing is widely recommended to prevent infectious disease transmission. However, little comparable evidence exists on the efficacy of handwashing ...

Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli

Prenyltransferases (PT) are a group of enzymes that catalyze chain elongation of allylic diphosphate using isopentenyl diphosphate (IPP) via multiple condensation reactions. DHDDS (dehydrodolichyl diphosphate synthase) is a eukaryotic long-chain cis-PT (forming cis double bonds from the condensation reaction) that catalyzes chain elongation of farnesyl diphosphate (FPP, an allylic diphosphate) via multiple condensations with isopentenyl diphosphate (IPP). DHDDS is of biomedical importance, as a non-conservative mutation (K42E) in the enzyme results in retinitis pigmentosa, ultimately leading to blindness. Therefore, the present protocol was developed in order to acquire large quantities of purified DHDDS, suitable for mechanistic studies. Here, the usage of protein fusion, optimized culture conditions and codon-optimization were used to allow the overexpression and purification of functionally active human DHDDS in E. coli. The described protocol is simple, cost-effective and time sparing. The homology of cis-PT among different species suggests that this protocol may be applied for other eukaryotic cis-PT as well, such as those involved in natural rubber synthesis.

Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli

A simple protocol for overexpression and purification of codon-optimized, human cis-prenyltransferase, under non-denaturing conditions, from Escherichia coli, is described, along with an enzymatic activity assay. This protocol can be generalized for production of other cis- prenyltransferase proteins in quantity and quality suitable for mechanistic studies.

Prenyltransferases (PT) are a group of enzymes that catalyze chain elongation of allylic diphosphate using isopentenyl diphosphate (IPP) via multiple ...

Ex Vivo Infection of Human Lymphoid Tissue and Female Genital Mucosa with Human Immunodeficiency Virus 1 and Histoculture

Histocultures allow studying intercellular interactions within human tissues, and they can be employed to model host-pathogen interactions under controlled laboratory conditions. Ex vivo infection of human tissues with human immunodeficiency virus (HIV), among other viruses, has been successfully used to investigate early disease pathogenesis, as well as a platform to test the efficacy and toxicity of antiviral drugs. In the present protocol, we explain how to process and infect with HIV-1 tissue explants from human tonsils and cervical mucosae, and maintain them in culture on top of gelatin sponges at the liquid-air interface for about two weeks. This non-polarized culture setting maximizes access to nutrients in culture medium and oxygen, although progressive loss of tissue integrity and functional architectures remains its main limitation. This method allows monitoring HIV-1 replication and pathogenesis using several techniques, including immunoassays, qPCR, and flow cytometry. Of importance, the physiologic variability between tissue donors, as well as between explants from different areas of the same specimen, may significantly affect experimental results. To ensure result reproducibility, it is critical to use an adequate number of explants, technical replicates, and donor-matched control conditions to normalize the results of the experimental treatments when compiling data from multiple experiments (i.e., conducted using tissue from different donors) for statistical analysis.

Ex Vivo Infection of Human Lymphoid Tissue and Female Genital Mucosa with Human Immunodeficiency Virus 1 and Histoculture

Infection of human tissues with human immunodeficiency virus (HIV) ex vivo provides a valuable 3D model of virus pathogenesis. Here, we describe a protocol to process and infect tissue specimens from human tonsils and female genital mucosae with HIV-1 and maintain them in culture at the liquid-air interface.

Histocultures allow studying intercellular interactions within human tissues, and they can be employed to model host-pathogen interactions under ...

Temporal Analysis of the Nuclear-to-cytoplasmic Translocation of a Herpes Simplex Virus 1 Protein by Immunofluorescent Confocal Microscopy

Infected cell protein 0 (ICP0) of herpes simplex virus 1 (HSV-1) is an immediate early protein containing a RING-type E3 ubiquitin ligase. It is responsible for the proteasomal degradation of host restrictive factors and the subsequent viral gene activation. ICP0 contains a canonical nuclear localization sequence (NLS). It enters the nucleus immediately after de novo synthesis and executes its anti-host defense functions mainly in the nucleus. However, later in infection, ICP0 is found solely in the cytoplasm, suggesting the occurrence of a nuclear-to-cytoplasmic translocation during HSV-1 infection. Presumably ICP0 translocation enables ICP0 to modulate its functions according to its subcellular locations at different infection phases. In order to delineate the biological function and regulatory mechanism of ICP0 nuclear-to-cytoplasmic translocation, we modified an immunofluorescent microscopy method to monitor ICP0 trafficking during HSV-1 infection. This protocol involves immunofluorescent staining, confocal microscope imaging, and nuclear vs. cytoplasmic distribution analysis. The goal of this protocol is to adapt the steady state confocal images taken in a time course into a quantitative documentation of ICP0 movement throughout the lytic infection. We propose that this method can be generalized to quantitatively analyze nuclear vs. cytoplasmic localization of other viral or cellular proteins without involving live imaging technology.

ICP0 undergoes nuclear-to-cytoplasmic translocation during HSV-1 infection. The molecular mechanism of this event is not known. Here we describe the use of confocal microscope as a tool to quantify ICP0 movement in HSV-1 infection, which lays the groundwork for quantitatively analyzing ICP0 translocation in future mechanistic studies.