Cell/cellular uptake

The first study was conducted to determine whether carotenoids and cholesterol share common pathways (transporters) for their intestinal absorption (During et al., 2005). Differentiated Caco-2 cells on membranes were incubated (16 h) with a carotenoid (1 pmol/L) with or without ezetimibe (EZ Zetia, an inhibitor of cholesterol transport), and with or without antibodies against the receptors, cluster determinant 36 (CD36) and scavenger receptor class B, type I (SR-BI). Carotenoid transport in Caco-2 cells (cellular uptake + secretion) was decreased by EZ (lOmg/L) as follows P-C and a-C (50% inhibition) P-cryptoxanthin and LYC (20%) LUT ZEA (1 1) (7%). EZ reduced cholesterol transport by 31%, but not retinol transport. P-Carotene transport was also inhibited by anti-SR-BI, but not by anti-CD36. The inhibitory effects of EZ and anti-SR-BI on P-C transport... 

To be used as delivery carriers for biomolecules, first it is essential to check whether the conjugates can effectively enter cells. Cellular uptake experiments were performed by using fluorescein isothiocyanate (FITC) conjugated LDH as a probe. Cells (5 x 105/ 1 ml) were incubated with LDH-FITC and its uptake was measured by flow cytometry. As shown in Figure 13.4, the cellular uptake was time and concentration dependent and... 

Acyclovir selectively inhibits viral DNA synthesis. It is preferentially activated in virally infected cells. Cellular uptake and initial phosphorylation are facilitated by the herpes virus thymidine kinase. The affinity of acyclovir for HSV... 

Figure 14.1. Fate of plasmid DNA in vivo after intravascular (left) or tissue (right) injection. Upon administration, plasmid DNA can be taken up by various cells, including mononuclear phagocytes such as macrophages. It also interacts with plasma proteins and extracellular matrix (ECM) components. In some cases, extravasation (intravascular route) or diffusion (tissue injection) is required for plasmid DNA to reach the target cell. Cellular uptake of DNA occurrs via an endocytotic route (solid lines) as well as a nonendocytotic route (dashed lines), depending on the vector and delivery method used for gene transfer. When endocytosis occurs, a means of endosomal escape is needed. Only plasmid DNA entering the nucleus has a chance to produce therapeutic protein.

Proteins embedded in the shell of lipoproteins. They serve as scaffold for assembly of the lipoprotein particle in the endoplasmic reticulum. In addition, they control metabolism of lipoproteins in the circulation by interaction with enzymes such as lipases. Finally, apolipoproteins determine cellular uptake of the particles by interaction with specific lipoprotein receptors expressed on the surface of target cells. 

Koppelhus U., Awasthi S.K., Zachar V., Holst H.U., Ebbesen P., Nielsen P. E. Cell-dependent differential cellular uptake of PNA, peptides, and PNA-pep-tide conjugates. Antisense Nucleic Acid Drug Dev. 2002 12 51-63. 

Oehlke and coworkers have described the cellular uptake properties of a simple a-hehcal amphipathic model peptide sequence (Lys-Leu-Ala-Leu-Lys-Leu-Ala-Leu-Lys-Ala-Leu-Lys-Ala-Ala-Leu-Lys-Leu-Ala) in the context of a drug delivery vehicle [72]. On the basis of the data presented, it was proposed that non-endocytosis mechanism(s) were involved in the uptake into mammalian cells. The similarity between our b2 aPNA-sequence to that of this amphipathic model peptide makes it tempting to suggest that a similar uptake mechanism is involved in the cellular uptake of aPNAs. Further experimentation is necessary to test this hypothesis. 

Pinocytosis is a property of all cells and leads to the cellular uptake of fluid and fluid contents. There are two types. Fluid-phase pinocytosis is a nonselective process in which the uptake of a solute by formation of small vesicles is simply proportionate to its concentration in the surrounding extracellular fluid. The formation of these vesicles is an extremely active process. Fi-... 

In contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of intestinal absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (taurocholate/oleic acid supplementation), differentiated Caco-2 cells were able to (1) take up carotenoids at the apical sides and incorporate them into CMs and (2) secrete them at the basolateral sides associated with CM fractions. Using this approach, the extent of absorption of P-carotene through Caco-2 cell monolayers after 16 hr of incubation was 11.2%, a value falling within the in vivo range (9 to 22%). ° - Of the total amount of P-carotene secreted, 78% was associated with the two CM fractions and 10% with the VLDL fraction. ... 

Fluid-phase uptake of macromolecules by cells in general is a slow process, and most administered macromolecules are eliminated from the host before any significant cellular uptake takes place. If, however, the macromolecule contains a moiety that is compatible with a receptor on a specific cell surface, then the macromolecule is attracted to the cell surface and the uptake is enhanced. This maximizes the opportunity for specific-cell capture. This type of cell-specific targeting has been developed to hepatocytes, with galactosamine to T lymphocytes, with anti-T cell antibodies and to mouse leukemia cells, with fucosylamine and other biomolecules. 

The advantageous effects of liposomal carrier systems include protection of compounds from metabolism or degradation, as well as enhanced cellular uptake. Liposome-mediated delivery of cytotoxic drugs to cells in culture has resulted in improved potency [58,59]. Prolonged release of encapsulated cargo has also been demonstrated [60,61]. More recently, liposomes with extended circulation half-lives and dose-independent pharmacokinetics (Stealth liposomes) [62] have shown promise in delivery of drugs that are normally very rapidly degraded. 

Since the ANPs are only slowly taken up by the cells and poorly absorbed following oral administration, some efforts have been directed toward the development of prodrugs (esters) that would be better taken up by the cells. These efforts have yielded the bispivaloyloxymethyl [bis(pom)] derivative of PMEA (Fig. 6) [56]. Bis(pom)-PMEA shows a cellular uptake increased more than a hundredfold, as well as fivefold better oral bioavailability than the parent compound [57], Both PMEA (given intravenously) and bis(pom)-PMEA (given perorally) are now in clinical trials in patients with AIDS. 

The entry of CL into cells may be essential for the cellular entry [232] or secretion [233] of some macromolecules such as diphtheria toxin and modeccin. Sandvig and Olsnes [232] studied the entry of diphtheria toxin and modeccin into Vero cells in pH 7.2 media containing 20 mM Hepes, 1 mM Ca(OH)2, 5 mM glucose,a sufficient amount of mannitol to ensure isotonicity, and varying concentrations of NaCl. The cellular uptake of 0.1 nM diphtheria toxin at the end of 50 min was strongly dependent on CL concentration. It was 0% at 0 mM NaCl, 25% of the 140 mM NaCl control at 2 mM NaCl, and 60% of the control at 70 mM NaCl. A similar trend was observed for modeccin, i.e., no transport at 0 mM NaCl, 20% of control at 0.05 mM NaCl, 60% of control at 0.1 mM NaCl, 80% of control at 0.5 mM NaCl, and 100% of control at 2 mM NaCl. 

The use of CL-free media required 100 times higher concentrations of the toxins for any cellular uptake. Furthermore, the entry of both toxins was denied when Vero cells were incubated in normal medium with inhibitors of CL entry, including 4-acetamido-4 -isothiocyanostilbene-2,2 -disulfonate (SITS), pyridoxal... 

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