Name: a model of experimental steatosis in vitro: hepatocyte cell culture in lipid overload-conditioned medium
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This work was funded by Consejo Nacional de Ciencia y Tecnolog&#237;a (Conacyt, CB-221137). Adriana Campos is a doctoral student at Programa de Doctorado en Ciencias Biom&#233;dicas, Universidad Nacional Aut&#243;noma de M&#233;xico, and was supported by Conacyt (CVU: 1002502).

1. Standard and conditioned medium preparation
<ol>
	<li>To prepare standard RPMI 1640, supplement RPMI 1640 culture medium with 10% (v/v) of fetal bovine serum (FBS, previously heat inactivated) and 1% (v/v) of Penicillin-Streptomycin solution. Store the medium at 4 &#176;C.Sterilize by using 0.22 &#181;m filters.</li>
	<li>To prepare palmitate stock solution, prepare a 50 mM solution of palmitate in the standard RPMI 1640 previously supplemented with 1% of bovine serum albumin (lipid free). A volume of 5-10 mL of thi...

<ol>
	<li>Younossi, Z. 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J., George, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MAFLD:+A+consensus-driven+proposed+nomenclature+for+metabolic+associated+fatty+liver+disease.">MAFLD: A consensus-driven proposed nomenclature for metabolic associated fatty liver disease.</a> Gastroenterology. 158 (7), 1999-2014 (2020).</li><li>Chalasani, 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=The+diagnosis+and+management+of+nonalcoholic+fatty+liver+disease:+Practice+guidance+from+the+American+association+for+the+study+of+liver+diseases.">The diagnosis and management of nonalcoholic fatty liver disease: Practice guidance from the American association for the study of liver diseases.</a> Hepatology. 67 (1), 328-357 (2018).</li><li>Calzadilla Bertot, L., Adams, L. 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M., 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=Effects+of+palmitic+acid+on+TNF-alpha-induced+cytotoxicity+in+SK-Hep-1+cells.">Effects of palmitic acid on TNF-alpha-induced cytotoxicity in SK-Hep-1 cells.</a> Toxicology In Vitro: An International Journal Published in Association with BIBRA. 26 (6), 783-790 (2012).</li><li>Stellavato, A., 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=In+vitro+assessment+of+nutraceutical+compounds+and+novel+nutraceutical+formulations+in+a+liver-steatosis-based+model.">In vitro assessment of nutraceutical compounds and novel nutraceutical formulations in a liver-steatosis-based model.</a> Lipids in Health and Disease. 17 (1), 24 (2018).</li><li>Pachikian, B. 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=Implication+of+trans-11,+trans-13+conjugated+linoleic+acid+in+the+development+of+hepatic+steatosis.">Implication of trans-11, trans-13 conjugated linoleic acid in the development of hepatic steatosis.</a> PLoS One. 13 (2), 0192447 (2018).</li><li>Ferreira, T., Rasband, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analyze.">Analyze.</a> ImageJ User Guide. , 132-135 (2012).</li><li>Geng, Y., Wu, Z., Buist-Homan, M., Blokzijl, H., Moshage, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hesperetin+protects+against+palmitate-induced+cellular+toxicity+via+induction+of+GRP78+in+hepatocytes.">Hesperetin protects against palmitate-induced cellular toxicity via induction of GRP78 in hepatocytes.</a> Toxicology and Applied Pharmacology. , 404 (2020).</li><li>Geng, Y., 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=Protective+effect+of+metformin+against+palmitate-induced+hepatic+cell+death.">Protective effect of metformin against palmitate-induced hepatic cell death.</a> Biochimica et Biophysica Acta - Molecular Basis of Disease. 1866 (3), 165621 (2020).</li><li>Sarnyai, 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=Effect+of+cis-+and+trans-monounsaturated+fatty+acids+on+palmitate+toxicity+and+on+palmitate-induced+accumulation+of+ceramides+and+diglycerides.">Effect of cis- and trans-monounsaturated fatty acids on palmitate toxicity and on palmitate-induced accumulation of ceramides and diglycerides.</a> International Journal of Molecular Science. 21 (7), 2626 (2020).</li><li>Chen, J. 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This protocol is intended to provide a strategy to study steatosis in vitro. Cell culture is a powerful tool to study cellular, molecular, biochemical, and toxicological aspects of the cells exposed to different conditions. With this approach, steatosis can be visualized not only as a stage of the complex disease that is MAFLD, but also as the hepatocyte overexposure to lipids and the possible outcomes resulting from such exposure. Therefore, its application is not restricted to the physiopathology of MAFLD, but...

Fatty liver associated with metabolic dysfunction is highly prevalent worldwide1,2; it is estimated that up to 25% of the population is affected3. This disease previously known as non-alcoholic fatty liver disease (NAFLD), has updated its nomenclature to metabolic dysfunction associated fatty liver disease (MAFLD) to accurately reflect the pathogenesis related with obesity, insulin resistance, diabetes type 2, and dyslipidemia, as well as the possible managements of the disease3,4.
Regardless of the name, the disease includes a wide spectrum of histopathological changes characterized by abnormally high accumulation of lipids in the liver (&#62;5% of fat in the hepatocytes5) and might progress through the lipid accumulation typically found in simple steatosis to steatohepatitis, which in turn might lead to the development of fibrosis, cirrhosis, hepatocellular carcinoma, and liver failure5,6,7,8. Due to its increasing prevalence, MAFLD is expected to become the first indication of liver transplantation and the leading cause of hepatocellular carcinoma9.
Although it has been considered as a benign or mild form of fatty liver disease, hepatic steatosis is in fact the metabolic key in MAFLD10. Different metabolic pathways are affected by lipid accumulation in the liver, including but not limited to lipid synthesis, exportation, and metabolism10. Insulin resistance, oxidative stress, reticular stress, and cellular dysfunction are strongly associated to hepatic lipotoxicity11,12. On the other hand, fatty hepatocytes are the target of reactive oxygen species, rendering metabolites as lipid peroxides, protein carbonyls, and adducts of nucleic acids13. At the cellular level, fatty hepatocytes might undergo mitochondrial damage14, cellular senescence15, apoptosis16, pyroptosis12, and autophagia17, among other events.
Hepatocytes are highly responsible for metabolism, detoxification, and synthesis of a wide range of molecules. Many of these functions might be compromised by the lipid accumulation observed in steatosis. Therefore, it is of great importance to have reproducible tools that allow an accurate evaluation of steatosis. In this sense, in vitro models are readily applicable and highly reproducible. Steatosis in vitro has been used with different goals16,18,19. The HepG2 cells are widely used as hepatocyte cell line. It has advantages such as being easy to culture and well characterized. Perhaps, the only disadvantage of HepG2 cells is the fact that it is a carcinogenic cell line, so this must be considered when analyzing the outcomes. Here, the application of a mixture of fatty acids widely used in cell culture: palmitic acid (PA) and oleic acid (OA) is shown. Both PA and OA offer different outcomes in culture20. PA (C 16:0) is the most common saturated fatty acid obtained from the diet16. PA is considered as a biomarker of de-novo lipogenesis, a crucial step in the development of NAFLD21. PA is shown to be highly toxic22; therefore, it might not be recommended to induce steatosis in vitro. OA (C 18:1) is a monounsaturated fatty acid. In contrast to PA, OA has been suggested to possess anti-inflammatory and anti-oxidant properties, being able to counteract PA12. Both PA and OA are the main fatty acids present in the triglycerides, regardless of the condition of health or disease16. Table 1 provides examples of the hepatocyte culture with PA, OA, and their mixture, as well as the outcomes reported12,23,24,25,26,27. Other fatty acids have also been used in hepatocyte culture, including stearic acid (C 18:0)28,29,30, linoleic acid (C 18:1)28,30,31 and its conjugates (CLA)28,32, palmitoleic acid (C 16:1)29. However, their use is least frequently reported in the literature, perhaps because their hepatic abundance is lower than PA and OA16.
In conjunction, both fatty acids resemble steatosis in vitro, providing proliferating cells, with increased cell death and lower viability compared with control conditions. It is worth mentioning that the respective salts of these fatty acids are available and can be used as well. One of the main problems when assessing lipid overload in hepatocyte cell culture is given in the differentiation between toxicological models and a model that best represent steatosis. Many models can be accounted in the first case. In fact, the use of PA alone might be considered among them, and the high mortality is the most evident outcome12,16,23,24,25,26,27. The use of high doses even in the case of OA can also be considered as a toxicologic model. The protocol shown here is in higher accordance with steatosis development since it shows low mortality compared with that observed in other models and allows it to be followed during several days with progressive lipid accumulation as it occurs in NAFLD. The possibility to assess mild and severe steatosis through experimental conditions is considered another advantage.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Fatty&#160;acids</td>
			<td colspan="2">Conditions</td>
			<td colspan="2">Outcomes</td>
			<td>Reference</td>
		</tr>
		<tr>
			<td rowspan="3">PA</td>
			<td colspan="2">Concentration:&#160;200&#160;&#956;M</td>
			<td colspan="2">Lipid accumulation</td>
			<td rowspan="3">Yan et al, 201925.</td>
		</tr>
		<tr>
			<td colspan="2">Time exposure:&#160;24 h</td>
			<td colspan="2">Hepatocyte damage</td>
		</tr>
		<tr>
			<td colspan="2"></td>
			<td colspan="2">Transaminases elevation</td>
		</tr>
		<tr>
			<td rowspan="2">PA</td>
			<td colspan="2">Concentration:&#160;50, 100&#160;and&#160;200&#160;&#956;M</td>
			<td colspan="2" rowspan="2">Lipid accumulation</td>
			<td rowspan="2">Xing et al, 201924.</td>
		</tr>
		<tr>
			<td colspan="2">Time exposure:&#160;24 h</td>
		</tr>
		<tr>
			<td rowspan="2">PA</td>
			<td colspan="2">Concentration:&#160;250 &#956;M&#160;, 500 &#956;M&#160;, 750 &#956;M&#160; and 1,000&#160;&#956;M</td>
			<td colspan="2">Lipid accumulation</td>
			<td rowspan="2">Wang et al, 202026.</td>
		</tr>
		<tr>
			<td colspan="2">Time exposure:&#160;24 h</td>
			<td colspan="2">Progressive reduction of cell viability</td>
		</tr>
		<tr>
			<td rowspan="3">Mix of&#160;OA/PA</td>
			<td colspan="2">Concentration:&#160;1 mM</td>
			<td colspan="2">Lipid&#160;accumulation</td>
			<td rowspan="3">Xiao et al, 202027.</td>
		</tr>
		<tr>
			<td colspan="2">Time exposure:&#160;24 h</td>
			<td colspan="2">Does not report&#160;lipotoxicity</td>
		</tr>
		<tr>
			<td colspan="2">Rate:&#160;2OA:1PA</td>
			<td colspan="2"></td>
		</tr>
		<tr>
			<td rowspan="4">Mix of&#160;OA/PA</td>
			<td colspan="2">First stimulation with&#160;200 &#956;M&#160;&#160;and&#160;400&#160;&#956;M of PA&#160;and then second stimulation with&#160;200&#160;&#956;M of OA</td>
			<td colspan="2">Lipid&#160;accumulation.&#160;</td>
			<td rowspan="4">Zeng et al, 202012.</td>
		</tr>
		<tr>
			<td colspan="2">Concentration:400&#160;&#956;M PA: 200&#160;&#956;M OA</td>
			<td colspan="2">Evidence of&#160;lipotoxicity&#160;induced by PA was reduced by stimulation of OA.</td>
		</tr>
		<tr>
			<td colspan="2">Rate:&#160;2PA:1OA</td>
			<td colspan="2"></td>
		</tr>
		<tr>
			<td colspan="2">Time exposure:&#160;24 h</td>
			<td colspan="2"></td>
		</tr>
		<tr>
			<td rowspan="3">Mix of&#160;OA/PA</td>
			<td colspan="2">Concentration:&#160;400&#160;&#956;M PA: 200&#160;&#956;M OA</td>
			<td colspan="2" rowspan="3">Lipid accumulation</td>
			<td rowspan="3">Chen et al, 201823.</td>
		</tr>
		<tr>
			<td colspan="2">Rate:&#160;2PA:1OA</td>
		</tr>
		<tr>
			<td colspan="2">Time exposure:&#160;24 h</td>
		</tr>
		<tr>
			<td rowspan="3">Mix of&#160;OA/PA</td>
			<td colspan="2">Concentration&#8239;:50&#160;and 500&#160;&#956;M</td>
			<td colspan="2">Generation&#160;of&#160;two&#160;types of&#160;steatosis:&#160;mild&#160;steatosis&#160;and 
			&#160;severe&#160;steatosis.</td>
			<td rowspan="3">Campos and Guzm&#225;n 2021</td>
		</tr>
		<tr>
			<td colspan="2">Rate: 2PA:1OA</td>
			<td colspan="2">Simulates&#160;chronic&#160;exposition of&#160;lipid overload</td>
		</tr>
		<tr>
			<td colspan="2">Time exposure: 24 h, 2 days,3 days and 4 days.</td>
			<td colspan="2"></td>
		</tr>
	</tbody>
</table>
Table 1. Hepatocyte culture in steatogenic conditions. The table presents the type of fatty acid used, the conditions maintained, and the observed outcomes in hepatocyte culture. PA: Palmitic acid. OA: Oleic acid.
Finally, this model is applicable not only to the study of steatosis and fatty liver, but also to the hepatic metabolic, synthetic, and detoxification pathways in the context of steatosis. Also, in vitro induced steatosis might provide evidence for the identification of potential markers of the disease as well as therapeutic targets.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Biosafety cabinet</td>
			<td>ESCO Airstream</td>
			<td>AC2-452+C2:C26</td>
			<td>Class II&#160;Type A2&#160;Biological Safety Cabinet</td>
		</tr>
		<tr>
			<td>Bottle top filter</td>
			<td>Corning, US</td>
			<td>430513</td>
			<td>&#160;Non-pyrogenic, polystyrene, sterile. 1 filter/Bag. 0.22 &#956;m, 500 mL.</td>
		</tr>
		<tr>
			<td>Bovine serum albimun (BSA)</td>
			<td>Gold Biotechnology, US</td>
			<td>A-421-10</td>
			<td>BSA Fatty Acid Free for cell culture</td>
		</tr>
		<tr>
			<td>Culture media RPMI 1640</td>
			<td>ThermoFisher-Gibco, US</td>
			<td>31800-022</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (FBS)</td>
			<td>ThermoFisher-Gibco, US</td>
			<td>A4766801</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Hemocytometer</td>
			<td>Marienfeld, DE</td>
			<td>640010</td>
			<td>-</td>
		</tr>
		<tr>
			<td>HepG2 cell line</td>
			<td>ATCC, US</td>
			<td>HB-8065</td>
			<td>Hepatocellular carcinoma human cells.</td>
		</tr>
		<tr>
			<td>Humidified incubator</td>
			<td>Thermo Electronic Corporation,US</td>
			<td>Model: 3110</td>
			<td>Temperature (37 &#176;C &#177; 1 &#176;C), humidity (90% &#177; 5%) , CO2 (5% &#177; 1%)</td>
		</tr>
		<tr>
			<td>Inverted microscope Eclipse</td>
			<td>NIKON, JPN</td>
			<td>Model: TE2000-S</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Sigma-Aldrich, US</td>
			<td>I9030-4L</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Oil Red O Kit</td>
			<td>Abcam, US</td>
			<td>ab150678</td>
			<td>Kit for histological visualization of neutral fat.</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich, US</td>
			<td>P6148-500G</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Penicillin/streptomycin</td>
			<td>ThermoFisher-Gibco, US</td>
			<td>15140-122</td>
			<td>Antibiotics 10,000 U/mL Penicillin, 10,000 &#956;g/mL Streptomycin</td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td>Beckman, US</td>
			<td>Model: 360 PH/Temp/MV Meter</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline</td>
			<td>ThermoFisher-Gibco, US</td>
			<td>10010-023</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Serological Pipettes</td>
			<td>Sarstedt, AUS</td>
			<td>86.1253.001</td>
			<td>&#160;Non-pyrogenic, sterile, 5 mL</td>
		</tr>
		<tr>
			<td>Serological Pipettes</td>
			<td>Sarstedt, AUS</td>
			<td>&#160;86.1254.001</td>
			<td>&#160;Non-pyrogenic, sterile, 10 mL</td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma-Aldrich, US</td>
			<td>S5761-1KG</td>
			<td>Preparation of culture media</td>
		</tr>
		<tr>
			<td>Sodium oleate</td>
			<td>Santa Cruz Biotechnology, US</td>
			<td>sc-215879A</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Sodium palmitate</td>
			<td>Santa Cruz Biotechnology, US</td>
			<td>sc-215881</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Syring filter</td>
			<td>Corning, US</td>
			<td>431219</td>
			<td>&#160;Non-pyrogenic, sterile, 28 mm, 0.2 &#956;m.</td>
		</tr>
		<tr>
			<td>Trypan Blue</td>
			<td>Sigma-Aldrich, US</td>
			<td>T6146-25G</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Trypsin 0.05% /EDTA 0.53 mM</td>
			<td>Corning, US</td>
			<td>25-052-Cl</td>
			<td>-</td>
		</tr>
		<tr>
			<td>24 well cell culture cluster</td>
			<td>Corning, US</td>
			<td>3524</td>
			<td>Flat bottom with lid. Tissue culture treated. Nonpyrogenic, polystyrene, sterile. 1/Pack.</td>
		</tr>
		<tr>
			<td>96 well cell culture cluster</td>
			<td>Corning, US</td>
			<td>3599</td>
			<td>Flat bottom with lid. Tissue culture treated. Nonpyrogenic, polystyrene, sterile. 1/Pack.</td>
		</tr>
	</tbody>
</table>

a model of experimental steatosis in vitro: hepatocyte cell culture in lipid overload-conditioned medium

Metabolic dysfunction-associated fatty liver disease (MAFLD), previously known as non-alcoholic fatty liver disease (NAFLD), is the most prevalent liver disease worldwide due to its relationship with obesity, diabetes type 2, and dyslipidemia. Hepatic steatosis, the accumulation of lipid droplets in the liver parenchyma, is a key feature of the disease preceding the inflammation observed in steatohepatitis, fibrosis, and end-stage liver disease. Lipid accumulation in hepatocytes might interfere with proper metabolism of xenobiotics and endogenous molecules, as well as to induce cellular processes leading to the advance of the disease. Although the experimental study of steatosis can be performed in vivo, in vitro approaches to the study of steatosis are complementary tools with different advantages. Hepatocyte culture in lipid overload-conditioned medium is an excellent reproducible option for the study of hepatic steatosis allowing the identification of cellular processes related to lipid accumulation, such as oxidative and reticular stresses, autophagia, proliferation, cell death, etcetera, as well as other testing including drug effectiveness, and toxicological testing, among many other possible applications. Here, it was aimed to describe the methodology of hepatocyte cell culture in lipid overload-conditioned medium. HepG2 cells were cultured in RMPI 1640 medium conditioned with sodium palmitate and sodium oleate. Importantly, the ratio of these two lipids is crucial to favor lipid droplet accumulation, while maintaining cell proliferation and a moderate mortality rate, as occurs in the liver during the disease. The methodology, from the preparation of the lipid solution stocks, mixture, addition to the medium, and hepatocyte culture is shown. With this approach, it is possible to identify lipid droplets in the hepatocytes that are readily observable by Oil-red O staining, as well as curves of proliferation/mortality rates.

Hepatocytes cultured in the steatogenic medium display growth all over the surface of the well; however, fatty hepatocytes show lower growth rate compared with cells cultured in control medium. The proposed ratio and concentration of OA and PA, guarantee cell survival during culture. Seeding 1 x 105 cells per well in 24-well plates provides optimum confluence as shown in Figure 1.
Viability in cultured cells was lower in the steatogenic groups, Mild and...

Watch this Scientific Journal Video about A Model of Experimental Steatosis In Vitro: Hepatocyte Cell Culture in Lipid Overload-Conditioned Medium at JoVE.com

A Model of Experimental Steatosis In Vitro: Hepatocyte Cell Culture in Lipid Overload-Conditioned Medium

This protocol is intended to be a tool to study steatosis and the molecular, biochemical, cellular changes produced by the over exposure of hepatocytes to lipids in vitro.

A Model of Experimental Steatosis In Vitro: Hepatocyte Cell Culture in Lipid Overload-Conditioned Medium

Metabolic dysfunction-associated fatty liver disease (MAFLD), previously known as non-alcoholic fatty liver disease (NAFLD), is the most prevalent liver ...

This protocol is applicable to the study of liver steatosis as well as to the hepatic, metabolic, synthetic, and the toxification pathways in the context of steatosis. The main advantages of this method are its reproducibility and the short time needed to obtain results. Add in the fact that it offers two levels of steatosis, mild, and severe.In vitro induced steatosis might provide evidence for the identification of potential markers for the diagnosis of the disease, as well as therapeutic targets. This method is meant to be applied in the steatosis result. However, it can be adjusted to a wide range of different cells affected by lipid over-exposures, like during obesity and lipidemia.Prepare standard RPMI 1640. Supplement RPMI 1640 culture medium with 10%of heat activated FBS, and 1%of penicillin streptomycin solution. Sterilize it by using 0.22 micrometer filters and store the supplement at four degrees Celsius.To prepare a palmitate stock solution prepare a 50 millimolar solution of palmitate in the standard RPMI 1640 supplemented with 1%of lipid free BSA. Sterilize about five to ten milliliters of the stock solution by using 0.22 micrometer filters and store at four degrees Celsius protected from light for up to one month. To prepare oleate stock solution prepare a 50 millimolar solution of oleate in the supplemented RPMI 1640.And sterilize the stock solution by using 0.22 micrometer filters. Store it at minus 20 degrees Celsius, protected from light for up to one month. To prepare steatogenic medium from the previously prepared stocks, prepare 100 millimeters of a 50 micromolar mix of one part palmitate and two part oleate.For mild levels, pour a 500 micromolar mix of one part palmitate and two part oleate for severe levels in standard RPMI 1640. And sterilize using 0.22 micrometer filters. Store at four degrees Celsius for up to one week.Alternatively, to prepare stock solutions with the respective fatty acids by using free lipid albumin, dissolve either palmitate or oleate in two milliliters of absolute ethanol and then mix in the final volume of standard RPMI 1640. Dissolve oleate directly by storing in standard RPMI 1640 culture medium. Allow evaporation of ethanol by incubating in a water bath at 70 degrees Celsius and mix thoroughly.Sterilize both stock solutions using 0.22 micrometer filters and store the palmitate stock solution at four degrees Celsius. And oleate stock solution at minus 20 degrees Celsius. Seat 0.1 million Hep G2 cells per well in a 24-well plate.Add one milliliter of standard RPMI 1640. Pre-incubate at 37 degrees Celsius and 5%carbon dioxide for 24 hours, allowing cell attachment. After pre culture, discard the standard RPMI 1640 medium.And add the steatogenic medium. Discard the supernatant and add a fresh steatogenic medium every 24 hours. To perform viability and morphology assessment, discard the supernatant and detach cells from the well by adding 500 microliters of 0.05%trypsin EDTA.Incubate for five minutes at 37 degrees Celsius and 5%carbon dioxide. Collect the resuspended cells in a micro tube. And centrifuge at 300 times G.Then discard the supernatant, add a 200 microliters of standard RPMI 1640, and resuspend the cells.Add 15 microliters of 0.4%of trypan blue solution in a fresh micro tube. Add and mix 15 microliters of the previous cell suspension. Count the stained and non stained cells in a hemocytometer and calculate the viability and mortality rates.Put a cell culture cover slip in every well in a 24-well plate and seed Hep G2 cells as described in the text manuscript. After the appropriate incubation, wash the cells with one milliliter of PBS and discard the supernatant. Mix them with one milliliter of 4%paraformaldehyde in PBS and incubate for one hour at room temperature.Discard the excess paraformaldehyde and rinse the cells with one milliliter of distilled water. Then add one milliliter of 70%isopropanol and incubate for five minutes. Discard the excess isopropanol and add one milliliter of Oil-Red O solution and incubate for 30 minutes.Discard the excess Oil-Red O solution, and then rinse with one milliliter of distilled water. Observe the cells under the microscope at a magnification of 400x. Randomly select and capture photographs of 10 optical fields from the complete area of the well.Repeat the imaging for every well. To assess the percentage of red stained area, open ImageJ software and import required files, then click on adjust and using the color threshold"tool, define the hue parameter for red color detection. Then adjust saturation and brightness for the image.Compare the stained area with the complete area of the optical field, using the analyze particles"tool and calculate the average percentage of every well. Seating 0.1 million hepatocytes per well in 24-well plates provides optimum confluence. Viability progressively diminished as time of the culture increased, reaching the lowest of 60%at four days in severe steatosis.Accordingly, the mortality rate was higher in hepatocytes cultured in the steatogenic conditions. And it progressively increased with the time of exposure to lipids. Cell numbers progressively increased as a result of proliferation.However, proliferation rate was lower in mild steatosis at three and four days. In contrast, severe steatosis was associated with lower proliferation by 24 hours. Staining cells with Oil-Red O demonstrated at least a twofold increase of lipid droplets in cells cultured under steatogenic conditions.Intracellular fat increased according to the time of exposure of culture in the steatogenic medium. In mild steatosis, lipid contents were increased from day two, whereas in severe steatosis they were significantly high starting at 24 hours. Cell culture requires previous experience.Culturing Hep G2 cells in a standard condition prior to using this protocol could be helpful. Preparation of the fatty-acid stock is also a crucial point. Palmitic acid is solid at room temperature, and it needs to be warmed before its management.This method should allow the molecular analysis of different pathways, including, but not limited to proliferation, apoptosis, autophagia, oxidative stress and pharmacologic and toxicologic analysis.

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Medicine

Multi-photon Imaging of Tumor Cell Invasion in an Orthotopic Mouse Model of Oral Squamous Cell Carcinoma

Loco-regional invasion of head and neck cancer is linked to metastatic risk and presents a difficult challenge in designing and implementing patient management strategies. Orthotopic mouse models of oral cancer have been developed to facilitate the study of factors that impact invasion and serve as model system for evaluating anti-tumor therapeutics. In these systems, visualization of disseminated tumor cells within oral cavity tissues has typically been conducted by either conventional histology or with in vivo bioluminescent methods. A primary drawback of these techniques is the inherent inability to accurately visualize and quantify early tumor cell invasion arising from the primary site in three dimensions. Here we describe a protocol that combines an established model for squamous cell carcinoma of the tongue (SCOT) with two-photon imaging to allow multi-vectorial visualization of lingual tumor spread. The OSC-19 head and neck tumor cell line was stably engineered to express the F-actin binding peptide LifeAct fused to the mCherry fluorescent protein (LifeAct-mCherry). Fox1nu/nu mice injected with these cells reliably form tumors that allow the tongue to be visualized by ex-vivo application of two-photon microscopy. This technique allows for the orthotopic visualization of the tumor mass and locally invading cells in excised tongues without disruption of the regional tumor microenvironment. In addition, this system allows for the quantification of tumor cell invasion by calculating distances that invaded cells move from the primary tumor site. Overall this procedure provides an enhanced model system for analyzing factors that contribute to SCOT invasion and therapeutic treatments tailored to prevent local invasion and distant metastatic spread. This method also has the potential to be ultimately combined with other imaging modalities in an in vivo setting.

A comprehensive overview of the techniques involved in generating a mouse model of oral cancer and quantitative monitoring of tumor invasion within the tongue through multi-photon microscopy of labeled cells is presented. This system can serve as a useful platform for the molecular assessment and drug efficacy of anti-invasive compounds.

Loco-regional invasion of head and neck cancer is linked to metastatic risk and presents a difficult challenge in designing and implementing patient ...

Stem Cell Transplantation in an in vitro Simulated Ischemia/Reperfusion Model

Stem cell transplantation protocols are finding their way into clinical practice1,2,3. Getting better results, making the protocols more robust, and finding new sources for implantable cells are the focus of recent research4,5. Investigating the effectiveness of cell therapies is not an easy task and new tools are needed to investigate the mechanisms involved in the treatment process6. We designed an experimental protocol of ischemia/reperfusion in order to allow the observation of cellular connections and even subcellular mechanisms during ischemia/reperfusion injury and after stem cell transplantation and to evaluate the efficacy of cell therapy. H9c2 cardiomyoblast cells were placed onto cell culture plates7,8. Ischemia was simulated with 150 minutes in a glucose free medium with oxygen level below 0.5%. Then, normal media and oxygen levels were reintroduced to simulate reperfusion. After oxygen glucose deprivation, the damaged cells were treated with transplantation of labeled human bone marrow derived mesenchymal stem cells by adding them to the culture. Mesenchymal stem cells are preferred in clinical trials because they are easily accessible with minimal invasive surgery, easily expandable and autologous. After 24 hours of co-cultivation, cells were stained with calcein and ethidium-homodimer to differentiate between live and dead cells. This setup allowed us to investigate the intercellular connections using confocal fluorescent microscopy and to quantify the survival rate of postischemic cells by flow cytometry. Confocal microscopy showed the interactions of the two cell populations such as cell fusion and formation of intercellular nanotubes. Flow cytometry analysis revealed 3 clusters of damaged cells which can be plotted on a graph and analyzed statistically. These populations can be investigated separately and conclusions can be drawn on these data on the effectiveness of the simulated therapeutical approach.

Stem Cell Transplantation in an in vitro Simulated Ischemia/Reperfusion Model

We demonstrate how to set up an in vitro ischemia/reperfusion model and how to evaluate the effect of stem cell therapy on postischemic cardiac cells.

Stem cell transplantation protocols are finding their way into clinical practice1,2,3. Getting better results, making the protocols more robust, and ...

Assessing Teratogenic Changes in a Zebrafish Model of Fetal Alcohol Exposure

Fetal alcohol syndrome (FAS) is a severe manifestation of embryonic exposure to ethanol. It presents with characteristic defects to the face and organs, including mental retardation due to disordered and damaged brain development. Fetal alcohol spectrum disorder (FASD) is a term used to cover a continuum of birth defects that occur due to maternal alcohol consumption, and occurs in approximately 4% of children born in the United States. With 50% of child-bearing age women reporting consumption of alcohol, and half of all pregnancies being unplanned, unintentional exposure is a continuing issue2. In order to best understand the damage produced by ethanol, plus produce a model with which to test potential interventions, we developed a model of developmental ethanol exposure using the zebrafish embryo. Zebrafish are ideal for this kind of teratogen study3-8. Each pair lays hundreds of eggs, which can then be collected without harming the adult fish. The zebrafish embryo is transparent and can be readily imaged with any number of stains. Analysis of these embryos after exposure to ethanol at different doses and times of duration and application shows that the gross developmental defects produced by ethanol are consistent with the human birth defect. Described here are the basic techniques used to study and manipulate the zebrafish FAS model.

In order to understand the molecular mechanisms of the ethanol-induced developmental damage, we have developed a zebrafish model of ethanol exposure and are exploring the physical, cellular, and genetic alterations that occur after ethanol exposure1. We then seek to find potential interventions and rapidly test them in this animal model.

Fetal alcohol syndrome (FAS) is a severe manifestation of embryonic exposure to ethanol. It presents with characteristic defects to the face and organs, ...

In vitro Mesothelial Clearance Assay that Models the Early Steps of Ovarian Cancer Metastasis

Ovarian cancer is the fifth leading cause of cancer related deaths in the United States1. Despite a positive initial response to therapies, 70 to 90 percent of women with ovarian cancer develop new metastases, and the recurrence is often fatal2. It is, therefore, necessary to understand how secondary metastases arise in order to develop better treatments for intermediate and late stage ovarian cancer. Ovarian cancer metastasis occurs when malignant cells detach from the primary tumor site and disseminate throughout the peritoneal cavity. The disseminated cells can form multicellular clusters, or spheroids, that will either remain unattached, or implant onto organs within the peritoneal cavity3 (Figure 1, Movie 1). 
All of the organs within the peritoneal cavity are lined with a single, continuous, layer of mesothelial cells4-6 (Figure 2). However, mesothelial cells are absent from underneath peritoneal tumor masses, as revealed by electron micrograph studies of excised human tumor tissue sections3,5-7 (Figure 2). This suggests that mesothelial cells are excluded from underneath the tumor mass by an unknown process. 
Previous in vitro experiments demonstrated that primary ovarian cancer cells attach more efficiently to extracellular matrix than to mesothelial cells8, and more recent studies showed that primary peritoneal mesothelial cells actually provide a barrier to ovarian cancer cell adhesion and invasion (as compared to adhesion and invasion on substrates that were not covered with mesothelial cells)9,10. This would suggest that mesothelial cells act as a barrier against ovarian cancer metastasis. The cellular and molecular mechanisms by which ovarian cancer cells breach this barrier, and exclude the mesothelium have, until recently, remained unknown. 
Here we describe the methodology for an in vitro assay that models the interaction between ovarian cancer cell spheroids and mesothelial cells in vivo (Figure 3, Movie 2). Our protocol was adapted from previously described methods for analyzing ovarian tumor cell interactions with mesothelial monolayers8-16, and was first described in a report showing that ovarian tumor cells utilize an integrin &#x2013;dependent activation of myosin and traction force to promote the exclusion of the mesothelial cells from under a tumor spheroid17. This model takes advantage of time-lapse fluorescence microscopy to monitor the two cell populations in real time, providing spatial and temporal information on the interaction. The ovarian cancer cells express red fluorescent protein (RFP) while the mesothelial cells express green fluorescent protein (GFP). RFP-expressing ovarian cancer cell spheroids attach to the GFP-expressing mesothelial monolayer. The spheroids spread, invade, and force the mesothelial cells aside creating a hole in the monolayer. This hole is visualized as the negative space (black) in the GFP image. The area of the hole can then be measured to quantitatively analyze differences in clearance activity between control and experimental populations of ovarian cancer and/ or mesothelial cells. This assay requires only a small number of ovarian cancer cells (100 cells per spheroid X 20-30 spheroids per condition), so it is feasible to perform this assay using precious primary tumor cell samples. Furthermore, this assay can be easily adapted for high throughput screening.

In vitro Mesothelial Clearance Assay that Models the Early Steps of Ovarian Cancer Metastasis

The mesothelial clearance assay described here takes advantage of fluorescently labeled cells and time-lapse video microscopy to visualize and quantitatively measure the interactions of ovarian cancer multicellular spheroids and mesothelial cell monolayers. This assay models the early steps of ovarian cancer metastasis.

Ovarian cancer is the fifth leading cause of cancer related deaths in the United States1. Despite a positive initial response to therapies, 70 to 90 ...

Excitotoxic Stimulation of Brain Microslices as an In vitro Model of Stroke

Examining molecular mechanisms involved in neuropathological conditions, such as ischemic stroke, can be difficult when using whole animal systems. As such, primary or &#39;neuronal-like&#39; cell culture systems are commonly utilized. While&#160;these systems are relatively easy to work with, and are useful model systems in which various functional outcomes (such as cell death) can be readily quantified, the examined outcomes and pathways in cultured immature neurons (such as excitotoxicity-mediated cell death pathways) are not necessarily the same as those observed in mature brain, or in intact tissue. Therefore, there is the need to develop models in which cellular mechanisms in mature neural tissue can be examined. We have developed an in vitro technique that can be used to investigate a variety of molecular pathways in intact nervous tissue. The technique described herein utilizes rat cortical tissue, but this technique can be adapted to use tissue from a variety of species (such as mouse, rabbit, guinea pig, and chicken) or brain regions (for example, hippocampus, striatum, etc.). Additionally, a variety of stimulations/treatments can be used (for example, excitotoxic, administration of inhibitors, etc.). In conclusion, the brain slice model described herein can be used to examine a variety of molecular mechanisms involved in excitotoxicity-mediated brain injury.

Excitotoxic Stimulation of Brain Microslices as an In vitro Model of Stroke

We have developed a brain slice model which can be used to examine molecular mechanisms involved in excitotoxicity-mediated brain injury.&#160;This technique generates viable mature brain tissue and reduces animal numbers required for experimentation, whilst keeping the neuronal circuitry, cellular interactions, and postsynaptic compartments partly intact.

Examining molecular mechanisms involved in neuropathological conditions, such as ischemic stroke, can be difficult when using whole animal systems. As ...

Neural Stem Cell Transplantation in Experimental Contusive Model of Spinal Cord Injury

Spinal cord injury is a devastating clinical condition, characterized by a complex of neurological dysfunctions. Animal models of spinal cord injury can be used both to investigate the biological responses to injury and to test potential therapies. Contusion or compression injury delivered to the surgically exposed spinal cord are the most widely used models of the pathology. In this report the experimental contusion is performed by using the Infinite Horizon (IH) Impactor device, which allows the creation of a reproducible injury animal model through definition of specific injury parameters. Stem cell transplantation is commonly considered a potentially useful strategy for curing this debilitating condition. Numerous studies have evaluated the effects of transplanting a variety of stem cells. Here we demonstrate an adapted method for spinal cord injury followed by tail vein injection of cells in CD1 mice. In short, we provide procedures for: i) cell labeling with a vital tracer, ii) pre-operative care of mice, iii) execution of a contusive spinal cord injury, and iv) intravenous administration of post mortem neural precursors. This contusion model can be utilized to evaluate the efficacy and safety of stem cell transplantation in a regenerative medicine approach.

Spinal cord injury is a traumatic condition that causes severe morbidity and high mortality. In this work we describe in detail a contusion model of spinal cord injury in mice followed by a transplantation of neural stem cells.

Spinal cord injury is a devastating clinical condition, characterized by a complex of neurological dysfunctions. Animal models of spinal cord injury can ...

Optimized Analysis of In Vivo and In Vitro Hepatic Steatosis

Establishing a system of procedures to qualitatively and quantitatively characterize in vivo and in vitro hepatic steatosis is important for metabolic study in the liver. Here, numerous assays are described to comprehensively measure the phenotype and parameters of hepatic steatosis in mouse and hepatocyte models. 
Combining the physiological, histological, and biochemical methods, this system can be used to assess the progress of hepatic steatosis. In vivo, the measurements of body weight and nuclear magnetic resonance (NMR) provide a general understanding of mice in a non-invasive manner. Hematoxylin and Eosin (H&amp;E) and Oil Red O staining determine the histological morphology and lipid deposition of liver tissue under nutrient overload conditions, such as high-fat diet feeding. Next, the total lipid contents are isolated by chloroform/methanol extraction, which are followed by a biochemical analysis for triglyceride and cholesterol. Moreover, mouse primary hepatocytes are treated with high glucose plus insulin to stimulate lipid accumulation, an efficient in vitro model to mimic diet-induced hyperglycemia and hyperinsulinemia in vivo. Then, the lipid deposition is measured by Oil Red O staining and chloroform/methanol extraction. Oil Red O staining determines intuitive hepatic steatotic phenotypes, while the lipid extraction analysis determines the parameters that can be analyzed statistically. The present protocols are of interest to scientists in the fields of fatty liver diseases, insulin resistance, and type 2 diabetes.

Optimized Analysis of In Vivo and In Vitro Hepatic Steatosis

Here, optimized methods to generate in vivo and in vitro models of hepatic steatosis and to analyze the steatotic phenotypes and related physiological parameters are described.

Establishing a system of procedures to qualitatively and quantitatively characterize in vivo and in vitro hepatic steatosis is important for metabolic ...

Using In Vitro Live-cell Imaging to Explore Chemotherapeutics Delivered by Lipid-based Nanoparticles

Conventional imaging techniques can provide detailed information about cellular processes. However, this information is based on static images in an otherwise dynamic system, and successive phases are easily overlooked or misinterpreted. Live-cell imaging and time-lapse microscopy, in which living cells can be followed for hours or even days in a more or less continuous fashion, are therefore very informative. The protocol described here allows for the investigation of the fate of chemotherapeutic nanoparticles after the delivery of doxorubicin (dox) in living cells. Dox is an intercalating agent that must be released from its nanocarrier to become biologically active. In spite of its clinical registration for more than two decades, its uptake, breakdown, and drug release are still not fully understood. This article explores the hypothesis that lipid-based nanoparticles are taken up by the tumor cells and are slowly degraded. Released dox is then translocated to the nucleus. To prevent fixation artifacts, live-cell imaging and time-lapse microscopy, described in this experimental procedure, can be applied.

Using In Vitro Live-cell Imaging to Explore Chemotherapeutics Delivered by Lipid-based Nanoparticles

Live-cell imaging is a powerful tool to visualize dynamic processes. The examination of fixed cells provides only static pictures, which can lead to misinterpretation and confusion about the process. This work presents a method to study uptake, drug release, and intracellular localization of liposomal nanoparticles in living cells.

Conventional imaging techniques can provide detailed information about cellular processes. However, this information is based on static images in an ...

A Cell Culture Model of Resistance Arteries

The myoendothelial junction (MEJ), a unique signaling microdomain in small diameter resistance arteries, exhibits localization of specific proteins and signaling processes that can control vascular tone and blood pressure. As it is a projection from either the endothelial or smooth muscle cell, and due to its small size (on average, an area of ~1 &#181;m2), the MEJ is difficult to study in isolation. However, we have developed a cell culture model called the vascular cell co-culture (VCCC) that allows for in vitro MEJ formation, endothelial cell polarization, and dissection of signaling proteins and processes in the vascular wall of resistance arteries. The VCCC has a multitude of applications and can be adapted to suit different cell types. The model consists of two cell types grown on opposite sides of a filter with 0.4 &#181;m pores in which the in vitro MEJs can form. Here we describe how to create the VCCC via plating of cells and isolation of endothelial, MEJ, and smooth muscle fractions, which can then be used for protein isolation or activity assays. The filter with intact cell layers can be fixed, embedded, and sectioned for immunofluorescent analysis. Importantly, many of the discoveries from this model have been confirmed using intact resistance arteries, underscoring its physiological relevance.

A cell culture model of resistance arteries is described, allowing for the dissection of signaling pathways in endothelium, smooth muscle, or between endothelium and smooth muscle (the myoendothelial junction). The selective application of agonists or protein isolation, electron microscopy, or immunofluorescence can be utilized using this cell culture model.

The myoendothelial junction (MEJ), a unique signaling microdomain in small diameter resistance arteries, exhibits localization of specific proteins and ...

Dissection and Explant Culture of Murine Allantois for the In Vitro Analysis of Allantoic Attachment

The placenta is essential for the growth and development of mammalian embryos. For this reason, numerous genetic alterations and likely also environmental insults that disturb placenta development or function can cause early pregnancy loss in mice and humans. Nevertheless, simple in vitro assays to screen for potential effects on placenta formation are lacking. Here, we focus on modeling the first and critical step in placenta formation, which consists of the attachment of the allantois to the chorion. We describe a method to rapidly assess the attachment of allantoic explants on immobilized &#945;4&#946;1 integrin, which serves as a chorio-mimetic substrate.This in vitro approach enables a qualitative evaluation of the attachment and spreading behavior of multiple allantois explants at different consecutive time points. The protocol may be used to investigate the effect of targeted mouse mutations, drugs, or various environmental factors that have been linked to pregnancy complications or fetal loss on allantois attachment ex vivo.

Dissection and Explant Culture of Murine Allantois for the In Vitro Analysis of Allantoic Attachment

We describe an in vitro assay to model chorioallantoic attachment, the first step in placenta formation. The protocol demonstrates the dissection and explant culture of murine allantoides on immobilized &#945;4&#946;1 integrin. Allantois attachment is evaluated microscopically at pre-determined time points.

The placenta is essential for the growth and development of mammalian embryos. For this reason, numerous genetic alterations and likely also environmental ...