Använda Caco-2-celler för att studera lipidtransport av tarmen
Summary
Caco-2 cells can serve as an in vitro model to study the enterocyte transport of lipids, and lipid-soluble drugs/vitamins. The permeable membrane system separates the apical from the basolateral compartment, while the lentivirus expression system offers an effective gene overexpression method. The isolation of lipoproteins is confirmed by TEM.
Abstract
Studies of dietary fat absorption are generally conducted by using an animal model equipped with a lymph cannula. Although this animal model is widely accepted as the in vivo model of dietary fat absorption, the surgical techniques involved are challenging and expensive. Genetic manipulation of the animal model is also costly and time consuming. The alternative in vitro model is arguably more affordable, timesaving, and less challenging. Importantly, the in vitro model allows investigators to examine the enterocytes as an isolated system, reducing the complexity inherent in the whole organism model. This paper describes how human colon carcinoma cells (Caco-2) can serve as an in vitro model to study the enterocyte transport of lipids, and lipid-soluble drugs and vitamins. It explains the proper maintenance of Caco-2 cells and the preparation of their lipid mixture; and it further discusses the valuable option of using the permeable membrane system. Since differentiated Caco-2 cells are polarized, the main advantage of using the permeable membrane system is that it separates the apical from the basolateral compartment. Consequently, the lipid mixture can be added to the apical compartment while the lipoproteins can be collected from the basolateral compartment. In addition, the effectiveness of the lentivirus expression system in upregulating gene expression in Caco-2 cells is discussed. Lastly, this paper describes how to confirm the successful isolation of intestinal lipoproteins by transmission electron microscopy (TEM).
Introduction
Studier av intestinala absorptionen av fett och fettlösliga läkemedel och vitaminer kan utföras in vivo genom att använda en lymfa fistel modell 1 – 4. Kirurgiska tekniker som deltar är emellertid inte bara en utmaning, men också kostsamt. Även in vivo metoder baserade på fekal analys kan användas, används de huvudsakligen för att bestämma den procentuella upptag av mag-tarmkanalen 2,5. In vitro-modell som beskrivs i detta dokument är mer kostnadseffektiv, och tekniker som är utan tvekan mindre utmanande. Genetiska modifieringsstudier är också mer ekonomiskt och mindre tidskrävande när de utförs med hjälp av denna in vitro-modell.
Eftersom fettlösliga material som tas upp av enterocyter förpackas i lipoproteiner 6,7, är avgörande effektiviteten i denna in vitro-modell för att producera lipoproteiner. De två huvud intestinal lipoproteiner är kylomikroner och mycket low-density lipoprotein (VLDL). Kylomikroner, definierade som lipoproteiner med 80 nm eller mer i diameter, produceras strikt tunntarmen när lipider är högst närvarande i mag-lumen. Eftersom de är de största lipoproteiner, kylomikroner är möjligen de mest effektiva lipid transportörer. Denna modell in vitro, vilken är kapabel att producera kylomikroner 8, kan användas för att studera dietary fettabsorption, lipidlösligt vitamin absorption av tarmen, och oralt lipofilt läkemedel biotillgänglighet. Närvaron av lipidlösliga molekyler, vitaminer eller läkemedel i lipoproteinfraktionen är en indikator på deras absorption genom tunntarmen. Som tidigare diskuterats, kan denna modell användas för att förbättra oral lipofilt läkemedel biotillgänglighet 6.
Detta dokument beskriver hur Caco-2-celler bör bibehållas i membran eller regelbundna vävnadsodlingsskålar, hur lipid mixture för att stimulera lipoprotein produktion bör förberedas, hur lentivirus expressionssystem kan användas för att uppnå en effektiv uttryck, och hur de isolerade lipoproteiner bör analyseras.
Protocol
Representative Results
Discussion
I detta dokument, för att de två systemen som kan användas bibehålla Caco-2-celler beskrivs, nämligen den vanliga vävnadsodlingsskålen och det permeabla membranet. Fördelarna med att använda det permeabla membransystemet innefattar separationen av den apikala och basolaterala facken, och förmågan att inkubera lipidblandningen och samla lipoproteinet sekre samtidigt. Emellertid, det permeabla membranet skären är dyra, och deras polykarbonatmembran tillåter inte god cell synlighet. En av fördelarna med dett…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by the Seed Grant Award from California Northstate University College of Pharmacy (to AMN). The authors would like to thank California Northstate University College of Pharmacy for covering the publication cost of this article, and George Talbott for his help in editing this manuscript.
Materials
| DMEM | VWR | 16750-112 | Pre-warm the growth media in individual tissue culture dish before adding cells |
| FBS | Fisher | 3600511 | We do not heat inactivate our serum |
| Trypsin | VWR | 45000-660 | Cells can be washed with PBS prior to trypsin treatment |
| Permeable membrane system | Fisher | 7200173 | 10-cm dish, 3-mm pore size, polycarbonate membrane |
| 10 cm dish | Fisher | 08-772-E | Tissue culture dish |
| 15 cm dish | Fisher | 08-772-24 | Tissue culture dish |
| 24 well plate | Fisher | 12565163 | Tissue culture plate |
| Lipid-based transfection reagent | Fisher | PRE2691 | Can be substituted with other transfection reagent |
| Reduced serum media | Invitrogen | 11058021 | For transfection |
| pLL3.7 eGFP | Addgene | 11795 | https://www.addgene.org/11795/ |
| Bottle-top filter | Fisher | 9761120 | 0.45 mm pore |
| Polybrene | Fisher | NC9840454 | 10 mg/mL |
| Oleic acid | Sigma | 01383-5G | Prevent freeze-thaw cycle |
| Lecithin | Fisher | IC10214625 | Egg lecithin |
| Sodium taurocholate | Fisher | NC9620276 | Product discontinued; alternative catalog number: 50-121-7956 |
| Protease inhibitor cocktail tablet (EDTA-free) | Fisher | 5892791001 | Used mainly for samples that need TEM analysis |
| Polycarbonate ultracentrifuge tube | Fisher | NC9696153 | Reusing it multiple times will collapse the tube |
| Lid for ultracentrifuge tube | Fisher | NC9796914 | A tool is required to remove the tube/lid from rotor |
| Syringe | Fisher | 50-949-261 | Disposable |
| Syringe filter | Fisher | 09-719C | Pore size = 0.2 mm; nylon |
| Phosphotungstic acid | Fisher | AC208310250 | For preparing 2% phosphotungstic acid, pH 6.0 |
| Tweezer | Fisher | 50-238-62 | Extra fine and strong tips |
| Formvar/carbon grid | Fisher | 50-260-34 | Formvar/carbon film square grid 400 Copper |
References
- Drover, V. A., et al. CD36 deficiency impairs intestinal lipid secretion and clearance of chylomicrons from the blood. J Clin Invest. 115 (5), 1290-1297 (2005).
- Nauli, A. M., et al. CD36 is important for chylomicron formation and secretion and may mediate cholesterol uptake in the proximal intestine. Gastroenterology. 131 (4), 1197-1207 (2006).
- Nauli, A. M., Zheng, S., Yang, Q., Li, R., Jandacek, R., Tso, P. Intestinal alkaline phosphatase release is not associated with chylomicron formation. Am J Physiol Gastrointest Liver Physiol. 284 (4), G583-G587 (2003).
- Lo, C. -. M., et al. Why does the gut choose apolipoprotein B48 but not B100 for chylomicron formation. Am J Physiol Gastrointest Liver Physiol. 294 (1), G344-G352 (2008).
- Jandacek, R. J., Heubi, J. E., Tso, P. A novel, noninvasive method for the measurement of intestinal fat absorption. Gastroenterology. 127 (1), 139-144 (2004).
- Nauli, A. M., Nauli, S. M. Intestinal transport as a potential determinant of drug bioavailability. Curr Clin Pharmacol. 8 (3), 247-255 (2013).
- Tso, P., Nauli, A., Lo, C. M. Enterocyte fatty acid uptake and intestinal fatty acid-binding protein. Biochem Soc Trans. 32 (Pt 1), 75-78 (2004).
- Nauli, A. M., Sun, Y., Whittimore, J. D., Atyia, S., Krishnaswamy, G., Nauli, S. M. Chylomicrons produced by Caco-2 cells contained ApoB-48 with diameter of 80-200 nm. Physiol Rep. 2 (6), (2014).
- Rubinson, D. A., et al. A lentivirus-based system to functionally silence genes in primary mammalian cells, stem cells and transgenic mice by RNA interference. Nat Genet. 33 (3), 401-406 (2003).
- Li, M., Husic, N., Lin, Y., Snider, B. J. Production of lentiviral vectors for transducing cells from the central nervous system. J Vis Exp. (63), e4031 (2012).
- Pottekat, A., et al. Insulin biosynthetic interaction network component, TMEM24, facilitates insulin reserve pool release. Cell Rep. 4 (5), 921-930 (2013).
- Van Greevenbroek, M. M., van Meer, G., Erkelens, D. W. Effects of saturated, mono-, and polyunsaturated fatty acids on the secretion of apo B containing lipoproteins by Caco-2 cells. Atherosclerosis. 21 (1), 139-150 (1996).
- Levy, E., Yotov, W., Seidman, E. G., Garofalo, C., Delvin, E., Ménard, D. Caco-2 cells and human fetal colon: a comparative analysis of their lipid transport. Biochim Biophys Acta. 1439 (3), 353-362 (1999).
- Luchoomun, J., Hussain, M. M. Assembly and secretion of chylomicrons by differentiated Caco-2 cells. Nascent triglycerides and preformed phospholipids are preferentially used for lipoprotein assembly. J Biol Chem. 274 (28), 19565-19572 (1999).
