Features and Mechanisms
Early studies revealed that differentiated Caco-2 cells expressed several morphological and functional properties characteristic of small bowel enterocytes. Towards confluence they start to polarize acquiring a characteristic apical brush border with microvilli. Tight junctions form between adjacent cells, and they express enzyme activities typical of enterocytes, i.e. lactase, aminopeptidase N, sucrase-isomaltase and dipeptidylpeptidase IV. However, markers of colonocytes are also present in Caco-2 cells (Engle et al. 1998) (Table 10.1).
Table 10.1 Properties of Caco-2 cells
|
Growth |
Grows in culture as an adherent monolayer of epithelial cells |
|
Differentiation |
Takes 14–21 days after confluence under standard culture conditions |
|
Cell morphology |
Polarized cells with tight junctions and brush border at the apical side |
|
Electrical parameters |
High electrical resistance |
|
Digestive enzymes |
Expresses typical digestive enzymes, membrane peptidases and disaccharidases of the small intestine (lactase, aminopeptidase N, sucrase-isomaltase and dipeptidylpeptidase IV) |
|
Active transport |
Amino acids, sugars, vitamins, hormones |
|
Membrane ionic transport |
Na+/K+ ATPase, H+/K+ ATPase, Na+/H+ exchange, Na+/K+/Cl− cotransport, apical Cl− channels |
|
Membrane non-ionic transporters |
Permeability glycoprotein (P-gp, multidrug resistance protein), multidrug resistance-associated protein, lung cancer-associated resistance protein |
|
Receptors |
Vitamin B12, vitamin D3, EGFR (epidermal growth factor receptor), sugar transporters (GLUT1, GLUT2, GLUT3, GLUT5, SGLT1) |
|
Cytokine production |
IL-6, IL-8, TNFα, TGF-β1, thymic stromal lymphopoietin (TSLP), IL-15 |
Stability, Consistency and Reproducibility
During the 35 years that have passed since its establishment, Caco-2 cells have been propagated in a number of laboratories worldwide. Due to different culture conditions and different numbers of passages, Caco-2 cells have often acquired different properties. Thus, the expression of differentiation markers typical of enterocytes, change with increasing numbers of passages (Artursson et al. 2001). Also, parameters like transepithelial electric resistance (TEER) and proliferation rate have been reported to increase with passage number (Briske Andersson et al. 1997). It has also been documented that late passage cells may start growing in multilayers, a phenomenon that will affect TEER measurements, and make comparisons with results based on early passage cells difficult.
