Name: in vivo alkaline comet assay and enzyme-modified alkaline comet assay for measuring dna strand breaks and oxidative dna damage in rat liver
Uploaded: 2016-05-04T14:00:00
Description: Watch this Scientific Journal Video about In Vivo Alkaline Comet Assay and Enzyme-modified Alkaline Comet Assay for Measuring DNA Strand Breaks and Oxidative DNA Damage in Rat Liver at JoVE.com

This work was supported by the US Food and Drug Administration. We acknowledge the original publication of the CPA study by Elsevier B.V.: Ding W, Bishop ME, Peace MG, Davis KJ, White GA, Lyn-Cook LE, Manjanatha MG. Sex-specific dose-response analysis of genotoxicity in cyproterone acetate-treated F344 rats. Mutation Research 774: 1-7, 2014 (PMID: 25440904)

Ethics statement: Procedures involving animals have been approved by the Institutional Animal Care and Use Committee (IACUC) at the US FDA/National Center for Toxicological Research.
NOTE: The study design described here is based on the protocol developed by the Japanese Center for the Validation of Alternative Methods (JaCVAM) for their validation of the in vivo rodent alkaline comet assay18, and further modified based on recommendations in OECD guideline TG48919</sup...

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G., 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=Genotoxicity+of+doxorubicin+in+F344+rats+by+combining+the+comet+assay,+flow-cytometric+peripheral+blood+micronucleus+test,+and+pathway-focused+gene+expression+profiling.">Genotoxicity of doxorubicin in F344 rats by combining the comet assay, flow-cytometric peripheral blood micronucleus test, and pathway-focused gene expression profiling.</a> Environ Mol Mutagen. 55 (1), 24-34 (2014).</li><li>Smith, C. C., O'Donovan, M. R., Martin, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=hOGG1+recognizes+oxidative+damage+using+the+comet+assay+with+greater+specificity+than+FPG+or+ENDOIII.">hOGG1 recognizes oxidative damage using the comet assay with greater specificity than FPG or ENDOIII.</a> Mutagenesis. 21 (3), 185-190 (2006).</li><li>Collins, A. 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This protocol describes the concurrent measurement of both direct and oxidative DNA damage in rat liver at the single cell level. The general protocol is applicable to any tissue from which single cells or nuclei can be isolated with minimal processing-induced DNA damage (i.e., DNA damage induced not by the test agent, but by the handling and processing of the animal tissues). In our research, we have conducted alkaline comet assays on cells from bone marrow7,9, stomach6, kidney9...

The alkaline comet assay measures DNA strand breaks at the single-cell level. Suspensions of single cells are embedded in agarose on a microscope slide and the cells lysed to form nucleoids, which contain supercoiled loops of DNA. Electrophoresis at pH&#62;13 results in the loss of supercoiling in DNA loops containing strand breaks, with the freed strands of DNA migrating toward the anode, creating comet-like structures that can be observed by fluorescence microscopy. Fragmented DNA migrates from the &#34;head&#34; of the comet into the &#34;tail&#34; based on the size of the fragment, and the relative fluorescence of the comet tail compared to the total intensity (head and tail) can be used to quantify DNA breakage1,2. The assay is simple, sensitive, versatile, rapid, and relatively inexpensive1. The detection of fragmented DNA caused by DNA-damaging agents is used an assay for quantifying DNA damage in cells or isolated nuclei from individual tissues of animals treated with potentially genotoxic material(s). Due to its advantages, the in vivo comet assay is recommended as a second in vivo genotoxicity assay (paired with the in vivo micronucleus assay) for conducting product safety evaluations in current International Conference on Harmonisation (ICH)3 and European Food Safety Authority (EFSA)4 regulatory guidelines. In our lab, we have employed the assay for evaluating in vivo DNA damage induced by food ingredients, pharmaceuticals, and nanomaterials5-10. Rat liver will be used as an example in this protocol, but the comet assay can be performed with other tissues/organs of experimental animals, as long as intact single cells can be isolated from the tissue.
Certain types of DNA damage are difficult to detect as DNA strand breaks without modifying the basic alkaline comet assay. In the case of oxidative DNA damage, strand breaks can be created at oxidative lesions in DNA by digesting with repair enzymes such as human 8-oxoguanine-DNA-N-glycosylase 1 (hOGG1, which creates breaks at 8-oxoguanine (8-oxoGua) and methyl-fapy-guanine11. Also, Endonuclease III (Endo III) creates breaks mainly at oxidized pyrimidines1. Thus, the addition of an enzyme-digestion step makes the assay a specific and sensitive method for measuring oxidative DNA damage in vivo12. Utilizing these assays, we have demonstrated toxicant-induced oxidative DNA damage in the liver of rats and mice6-8 and in the heart of rats10.
The alkaline comet assay has many applications in genetic toxicology and human biomonitoring: 1) as a follow-up in vivo assay for genotoxins identified by sensitive in vitro tests3,13, 2) to evaluate mechanisms of xenobiotic-induced DNA damage in multiple tissues14, 3) to investigate if a carcinogen operates using a genotoxic or a non-genotoxic mode of action (MOA)7, 4) to evaluate DNA damage repair15, 5) to investigate human diseases and occupational exposures 16, and 6) as a potential high-throughput screening assay for organ-specific genotoxicity17.

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		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Coverslips (No. 1, 24 x 50 mm)&#160;</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">12-544-14</td>
			<td style="width:215px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Microscope Slides</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">12-550-123</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Dimethylsulfoxide (DMSO)&#160;</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">67-68-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">EDTA, Disodium</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">BP120-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Phosphate buffered saline</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">ICN1860454</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:232px;">1X Hanks Balanced Salt Solution (HBSS) (Ca++, Mg++ free)&#160;</td>
			<td style="width:140px;">HyClone</td>
			<td style="width:156px;">SH30588.02</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">HEPES</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">BP310-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Low Melting Point Agarose (LMP)</td>
			<td style="width:140px;">Lonza</td>
			<td align="right" style="width:156px;">50081</td>
			<td>NuSieve GTG Agarose</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Normal Melting Agarose (NMA)&#160;</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">BP1356-100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">pH testing paper strips (pH 7.5-14)</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">M95873</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Potassium Cloride</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">7447-40-7</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Potassium Hydroxide</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">1310-58-3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">slide labels, (0.94 x 0.5 in.)</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">NC9822036</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Sodium Chloride (NaCl)&#160;</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">7647-14-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Sodium Hydroxide (NaOH)&#160;</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">1310-73-2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">SYBR&#8482; Gold&#160;</td>
			<td style="width:140px;">Invitrogen</td>
			<td style="width:156px;">S11494</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Triton X-100&#160;</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">9002-93-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Trizma Base&#160;</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">77-86-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">2.0 mL microcentrifuge tubes</td>
			<td style="width:140px;">Fisher</td>
			<td style="width:156px;">05-402-6</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Cell strainer (40 &#181;m)</td>
			<td style="width:140px;">Fisher</td>
			<td align="right" style="width:156px;">22363547</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">Endonuclease III (Nth)&#160;</td>
			<td style="width:140px;">New England Biolabs</td>
			<td style="width:156px;">M0268S</td>
			<td>Dilution 1:1000</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:232px;">hOGG1&#160;</td>
			<td style="width:140px;">New England Biolabs</td>
			<td style="width:156px;">M0241S</td>
			<td>Dilution 1:1000</td>
		</tr>
	</tbody>
</table>

in vivo alkaline comet assay and enzyme-modified alkaline comet assay for measuring dna strand breaks and oxidative dna damage in rat liver

Unrepaired DNA damage can lead to genetic instability, which in turn may enhance cancer development. Therefore, identifying potential DNA damaging agents is important for protecting public health. The in vivo alkaline comet assay, which detects DNA damage as strand breaks, is especially relevant for assessing the genotoxic hazards of xenobiotics, as its responses reflect the in vivo absorption, tissue distribution, metabolism and excretion (ADME) of chemicals, as well as DNA repair process. Compared to other in vivo DNA damage assays, the assay is rapid, sensitive, visual and inexpensive, and, by converting oxidative DNA damage into strand breaks using specific repair enzymes, the assay can measure oxidative DNA damage in an efficient and relatively artifact-free manner. Measurement of DNA damage with the comet assay can be performed using both acute and subchronic toxicology study designs, and by integrating the comet assay with other toxicological assessments, the assay addresses animal welfare requirements by making maximum use of animal resources. Another major advantage of the assays is that they only require a small amount of cells, and the cells do not have to be derived from proliferating cell populations. The assays also can be performed with a variety of human samples obtained from clinically or occupationally exposed individuals.

The in vivo alkaline comet assay was performed in conjunction with the enzyme-modified comet assay to measure both direct and oxidative DNA damage in the liver of rats treated with cyproterone acetate (CPA)5. CPA is a synthetic hormonal drug that induces rat liver tumors in a sex-specific manner, with five-fold higher doses needed to induce liver tumors in male rats compared to females24. We found that the direct DNA damage produced by CPA in the liver of ma...

Watch this Scientific Journal Video about In Vivo Alkaline Comet Assay and Enzyme-modified Alkaline Comet Assay for Measuring DNA Strand Breaks and Oxidative DNA Damage in Rat Liver at JoVE.com

In Vivo Alkaline Comet Assay and Enzyme-modified Alkaline Comet Assay for Measuring DNA Strand Breaks and Oxidative DNA Damage in Rat Liver

The alkaline comet assay measures DNA strand breaks in eukaryotic cells. By adding an Endonuclease III or human 8-oxoguanine-DNA-N-glycosylase digestion step, the assay can efficiently detect oxidative DNA damage. We describe methods for using these assays to detect DNA damage in rat liver.

In Vivo Alkaline Comet Assay and Enzyme-modified Alkaline Comet Assay for Measuring DNA Strand Breaks and Oxidative DNA Damage in Rat Liver

Unrepaired DNA damage can lead to genetic instability, which in turn may enhance cancer development. Therefore, identifying potential DNA damaging agents ...

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