Cellular uptake

Antimicrobial Activity. The elfamycins antimicrobial specificity and lack of toxicity in animals can be explained in view of species-dependent specificity of elfamycin binding to EE-Tu. Inefficient cellular uptake or the presence of a nonresponding EE-Tu were cited as responsible factors for the natural resistance in Halohacterium cutiruhrum (67), Lactobaci//us brevis (68), and in actinomycetes (5,69). The low activity of elfamycins against S. aureus was also attributed to an elfamycin-resistant EE-Tu system (70). However, cross-resistance with other antibacterial agents has not been observed (71). 

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. 

Cellular defense mechanisms against toxins (A multistep mechanism for elimination of toxic metabolites and xenobiotics. It involves various transport, oxidation, and conjugation steps.) are usually divided into several steps as it is visualized on Fig. 3. Organic anion transporting proteins (OATPs) are responsible for the cellular uptake of endogenous compounds and... 

Neurotransmitter transporters determine the neurotransmitter concentration in the interstitium. High-affinity transporters can efficiently remove neurotransmitter from the extracellular space because cellular uptake is typically coupled to the translocation of sodium ions. 

Peptoid-Based Drug Delivery and Molecular Transporters Cellular Uptake... 

Wender, P.A., Mitchell, D.J., Pelkey, E.T., Steinman, L., and Rothbard, J.B. Xhe design, synthesis, and evaluation of molecules that enable or enhance cellular uptake Peptoid molecular transporters. Proc. Nad. Acad. Sci. USA 2000, 97, 13003-13008. 

T.A. Beerman, and P.B. Dervan. Cellular uptake of N-methylpyrrole/N-methyli-midazole polyamide-dye conjugates. 

To obtain an increased intrinsic capacity to transgress biological membranes, a number of different modifications have been introduced to PNA. These modifications include conjugation of PNA to Hpophilic moieties [51, 97, 98], conjugation of PNA to certain so-caUed ceU-penetrating peptides [49, 55, 56, 66, 99-102] and conjugation to different moieties, which are supposed to be internahzed by specific cellular receptors [48, 103-105]. The work on cellular dehvery of PNA is, like the related work on ex vivo and in vivo effects of PNA, very difficult to summarize conclusively. First of all, the pronounced diversity of the reporter systems employed makes it impossible to directly compare the studies. Secondly, the widespread use of fluorescence studies in spite of the many inherent pitfalls of this technique makes it sometimes difficult to judge even qualitatively whether a presented result actually indicates cellular uptake. We have recently published a comprehensive review on cellular dehvery of PNA [82], with a more detailed assessment of the PNA dehvery hterature. 

Ljungstrom T., Knudsen H., Nielsen P.E. Cellular uptake of adamantyl conjugated peptide nucleic acids. Bioconjug. 

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. 

Basu S., Wickstrom E. Synthesis and characterization of a peptide nucleic acid conjugated to a D-peptide analog of insu-lin-like growth factor 1 for increased cellular uptake. Bioconjug. Chem. 1997 8 481-488. 

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. ... 

Kiefer, C. et al., A class B scavenger receptor mediates the cellular uptake of carotenoids iu Drosophila, Proc. Natl. Acad. ScL USA, 16, 10581, 2002. 

FIG. 15 Cellular entry and intracellular kinetics of the cationic lipid-DNA complexes. Cationic lipid-DOPE liposomes form electrostatic complexes with DNA, and, in this case, also transferrin (Tf) is incorporated. Cellular uptake by endoc5dosis and endosomal acidification can be blocked with cytochaiasin B and bafilomycin Aj, respectively. DNA is proposed to be released at the level of endosomal wall after fusion of the carrier lipids with endosomal bilayer. This process is facilitated by the formation of inverted hexagonal DOPE phase as illustrated in the lower corner on the right. After its release to the C5doplasm DNA may enter the nucleus. (From Ref. 253. By permission of Nature Publishing Group.)... 

Peptides have been used for the delivery of gene-based drugs. Several rationales have been utilized. Cationic peptides are used to neutralize the charges of DNA or oligonucleotide. These peptides include polylysines and polyarginines [241,244,245]. They form complexes with DNA or oligonucleotide, thereby resulting in enhanced cellular uptake. 

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. 

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