Dipeptide uptake and transport characteristics in rabbit tracheal epithelial cell layers cultured at an air interface

Modified biopolymer-dextrin based crosslinked hydrogels: application in controlled drug delivery

This review describes hydrogels and their classifications along with the synthesis and properties of biopolymer-dextrin based crosslinked hydrogels towards potential application in controlled drug delivery.

Crosslinked ionic polysaccharides for stimuli-sensitive drug delivery

Polysaccharides are gaining increasing attention as components of stimuli-responsive drug delivery systems, particularly since they can be obtained in a well characterized and reproducible way from the natural sources. Ionic polysaccharides can be readily crosslinked to render hydrogel networks sensitive to a variety of internal and external variables, and thus suitable for switching drug release on-off through diverse mechanisms. Hybrids, composites and grafted polymers can reinforce the responsiveness and widen the range of stimuli to which polysaccharide-based systems can respond. This review analyzes the state of the art of crosslinked ionic polysaccharides as components of delivery systems that can regulate drug release as a function of changes in pH, ion nature and concentration, electric and magnetic field intensity, light wavelength, temperature, redox potential, and certain molecules (enzymes, illness markers, and so on). Examples of specific applications are provided. The information compiled demonstrates that crosslinked networks of ionic polysaccharides are suitable building blocks for developing advanced externally activated and feed-back modulated drug delivery systems.

Drug transporters in the lung--do they play a role in the biopharmaceutics of inhaled drugs?

The role of transporters in drug absorption, distribution and elimination processes as well as in drug-drug interactions is increasingly being recognised. Although the lungs express high levels of both efflux and uptake drug transporters, little is known of the implications for the biopharmaceutics of inhaled drugs. The current knowledge of the expression, localisation and functionality of drug transporters in the pulmonary tissue and the few studies that have looked at their impact on pulmonary drug absorption is extensively reviewed. The emphasis is on transporters most likely to affect the disposition of inhaled drugs: (1) the ATP-binding cassette (ABC) superfamily which includes the efflux pumps P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs), breast cancer resistance protein (BCRP) and (2) the solute-linked carrier (SLC and SLCO) superfamily to which belong the organic cation transporter (OCT) family, the peptide transporter (PEPT) family, the organic anion transporter (OAT) family and the organic anion transporting polypeptide (OATP) family. Whenever available, expression and localisation in the intact human tissue are compared with those in animal lungs and respiratory epithelial cell models in vitro. The influence of lung diseases or exogenous agents on transporter expression is also mentioned.

Molecular mechanisms of pulmonary peptidomimetic drug and peptide transport

The aerosolic administration of peptidomimetic drugs could play a major role in the future treatment of various pulmonary and systemic diseases, because rational drug design offers the potential to specifically generate compounds that are transported efficiently into the epithelium by distinct carrier proteins such as the peptide transporters. From the two presently known peptide transporters, PEPT1 and PEPT2, which have been cloned from human tissues, the high-affinity transporter PEPT2 is expressed in the respiratory tract epithelium. The transporter is an integral membrane protein with 12 membrane-spanning domains and mediates electrogenic uphill peptide and peptidomimetic drug transport by coupling of substrate translocation to a transmembrane electrochemical proton gradient serving as driving force. In human airways, PEPT2 is localized to bronchial epithelium and alveolar type II pneumocytes, and transport studies revealed that both peptides and peptidomimetic drugs such as antibiotic, antiviral, and antineoplastic drugs are carried by the system. PEPT2 is also responsible for the transport of delta-aminolevulinic acid, which is used for photodynamic therapy and the diagnostics of pulmonary neoplasms. Based on the recent progress in understanding the structural requirements for substrate binding and transport, PEPT2 becomes a target for a rational drug design that may lead to a new generation of respiratory drugs and prodrugs that can be delivered to the airways via the peptide transporter.

Characterization of carnosine uptake and its physiological function in human intestinal epithelial Caco-2 cells

Carnosine (beta-Ala-L-His) is known to have the physiological functions of an antioxidant. Although dietary carnosine is thought to be absorbed across intestinal epithelial cells, the mechanism for this absorption is not yet well understood and its function in the intestinal tract is also obscure. The intestinal transport of carnosine was characterized in the present study by using human intestinal Caco-2 cells, and its physiological function in these cells was further examined. The carnosine uptake was proton-dependent, being activated by lowering the apical pH value. Its uptake was significantly inhibited by other dipeptides, whereas it was not inhibited by other amino acids. These characteristics of the carnosine uptake strongly suggest its transport into the cells via peptide transporter 1 (PepT1). Since carnosine has antioxidative activity, we studied its effect on the H2O2-induced secretion of inflammatory cytokines in Caco-2 cells. The H2O2 induced increase in IL-8 secretion was inhibited by a pretreatment with carnosine for 3 h, this inhibition being presented in a dose-dependent manner. These results suggest that carnosine had a protective effect against oxidative stress in intestinal epithelial cells.

High airway-to-blood transport of an opioid tetrapeptide in the isolated rat lung after aerosol delivery

The airway-to-blood absorption of the mu-selective opioid tetrapeptide agonist Tyr-D-Arg-Phe-Phe-NH(2) (MW 631) was investigated in the isolated, perfused, and ventilated rat lung model. The lung metabolism of the peptide was compared after airway and vascular delivery. The concentrations of the parent tetrapeptide and five of its metabolites in the perfusate and in bronchoalveolar lavage fluid were analyzed by LC-MS. The metabolism of the peptide was higher after delivery to the airways compared to vascular delivery. However, the tetrapeptide was highly transported from the air-to-blood side to an extent of 47.8 +/- 10.7% in 2 h. In conclusion, the results prompt investigations of the pulmonary route as a successful alternative to parenteral delivery for this tetrapeptide.

Distribution and function of the peptide transporter PEPT2 in normal and cystic fibrosis human lung

BACKGROUND

Aerosol administration of peptide based drugs has an important role in the treatment of various pulmonary and systemic diseases. The characterisation of pulmonary peptide transport pathways can lead to new strategies in aerosol drug treatment.

METHODS

Immunohistochemistry and ex vivo uptake studies were established to assess the distribution and activity of the beta-lactam transporting high affinity proton coupled peptide transporter PEPT2 in normal and cystic fibrosis human airway tissue.

RESULTS

PEPT2 immunoreactivity in normal human airways was localised to cells of the tracheal and bronchial epithelium and the endothelium of small vessels. In peripheral lung immunoreactivity was restricted to type II pneumocytes. In sections of cystic fibrosis lung a similar pattern of distribution was obtained with signals localised to endothelial cells, airway epithelium, and type II pneumocytes. Functional ex vivo uptake studies with fresh lung specimens led to an uptake of the fluorophore conjugated dipeptide derivative D-Ala-L-Lys-AMCA into bronchial epithelial cells and type II pneumocytes. This uptake was competitively inhibited by dipeptides and cephalosporins but not ACE inhibitors, indicating a substrate specificity as described for PEPT2.

CONCLUSIONS

These findings provide evidence for the expression and function of the peptide transporter PEPT2 in the normal and cystic fibrosis human respiratory tract and suggest that PEPT2 is likely to play a role in the transport of pulmonary peptides and peptidomimetics.

Localization of the peptide transporter PEPT2 in the lung: implications for pulmonary oligopeptide uptake

Pulmonary delivery of peptidomimetic antibiotics is frequently used for local drug therapy in pulmonary infections. Identification of transport pathways into airway epithelia can lead to new strategies of therapy. Here we describe the distribution of the beta-lactam-transporting high-affinity proton-coupled peptide transporter PEPT2 in mammalian lungs. Using reverse transcriptase-polymerase chain reaction and Northern blot analysis, PEPT2-mRNA was detected in lung extracts. The expression of PEPT2-mRNA and protein was localized to alveolar type II pneumocytes, bronchial epithelium, and endothelium of small arteries of rat lung by nonisotopic in situ hybridization and immunohistochemistry. In addition, transport studies using murine whole-organ preparations revealed transporter-mediated uptake of a fluorophore-conjugated dipeptide derivative into bronchial epithelial cells and type II pneumocytes. This transport was competitively inhibited by cephalosporins and dipeptides that are reported as PEPT2-carried substrates. Cell specificity of the PEPT2-mediated uptake pattern was confirmed by double labeling with Lycopersicon esculentum lectin. Together these data suggest that PEPT2 is the molecular basis for the transport of peptides and peptidomimetics in pulmonary epithelial cells. In conclusion PEPT2 may be an interesting target for pulmonary delivery of peptides and peptidomimetics.