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

Lung penetration and pneumococcal target binding of antibiotics in lower respiratory tract infection

OBJECTIVES

To achieve the therapeutic effects, antibiotics must penetrate rapidly into infection sites and bind to targets. This study reviewed updated knowledge on the ability of antibiotics to penetrate into the lung, their physicochemical properties influencing the pulmonary penetration and their ability to bind to targets on pneumococci.

METHODS

A search strategy was developed using PubMED, Web of Science, and ChEMBL. Data on serum protein binding, drug concentration, target binding ability, drug transporters, lung penetration, physicochemical properties of antibiotics in low respiratory tract infection (LRTI) were collected.

RESULTS

It was seen that infection site-to-serum concentration ratios of most antibiotics are >1 at different time points except for ceftriaxone, clindamycin and vancomycin. Most agents have proper physicochemical properties that facilitate antibiotic penetration. In antimicrobial-resistant Streptococcus pneumoniae, the binding affinity of antibiotics to targets mostly decreases compared to that in susceptible strains. The data on binding affinity of linezolid, clindamycin and vancomycin were insufficient. The higher drug concentration at the infection sites compared to that in the blood can be associated with inflammation conditions. Little evidence showed the effect of drug transporters on the clinical efficacy of antibiotics against LRTI.

CONCLUSIONS

Data on antibiotic penetration into the lung in LRTI patients and binding affinity of antibiotics for pneumococcal targets are still limited. Further studies are required to clarify the associations of the lung penetration and target binding ability of antibitotics with therapeutic efficacy to help propose the right antibiotics for LRTI.

Effect of Corticosteroids on Peptide Transporter 2 Function and Induction of Innate Immune Response by Bacterial Peptides in Alveolar Epithelial Cells

In the lung alveolar region, the innate immune system serves as an important host defense system. We recently reported that peptide transporter 2 (PEPT2) has an essential role in the uptake of bacterial peptides and induction of innate immune response in alveolar epithelial cells. In this study, we aimed to clarify the effects of corticosteroids on PEPT2 function and PEPT2-dependent innate immune response. NCI-H441 (H441) cells were used as an in vitro model of human alveolar type II epithelial cells, and the effects of dexamethasone (DEX) and budesonide (BUD) on the transport function of PEPT2 and the innate immune response induced by bacterial peptides were examined. PEPT2 function, estimated by measuring β-alanyl-Nε-(7-amino-4-methyl-2-oxo-2H-1-benzopyran-3-acetyl)-L-lysine (β-Ala-Lys-AMCA) uptake in H441 cells, was suppressed by treatment with DEX and BUD in a concentration- and time-dependent manner. The suppression of PEPT2 function was partially recovered by a glucocorticoid receptor antagonist. The expression of PEPT2 and nucleotide-binding oligomerization domain 1 (NOD1) mRNAs was suppressed by treatment with DEX and BUD, while PEPT2 protein level was not changed by these treatment conditions. Additionally, the increased mRNA expression of interleukin (IL)-8 and the increased secretion of IL-8 into the culture medium induced by bacterial peptides were also suppressed by treatment with these corticosteroids. Taken together, these results clearly suggest that corticosteroids suppress PEPT2 function and bacterial peptide-induced innate immune response in alveolar epithelial cells. Therefore, PEPT2- and NOD1-dependent innate immune response induced by bacterial peptides in the lung alveolar region may be suppressed during the inhaled corticosteroid therapy.

Taking leads out of nature, can nano deliver us from COVID-like pandemics?

The COVID-19 crisis has alerted the research community to re-purpose scientific tools that can effectively manage emergency pandemic situations. Researchers were never so desperate to discover a 'magic bullet' that has significant clinical benefits with minimal or no side effects. At the beginning of the pandemic, due to restricted access to traditional laboratory techniques, many research groups delved into computational screening of thousands of lead molecules that could inhibit SARS-CoV-2 at one or more stages of its infectious cycle. Several in silico studies on natural derivatives point out their potency against SARS-CoV-2 proteins. However, theoretical predictions and existing knowledge on related molecules reflect their poor oral bioavailability due to biotransformation in the gut and liver. Nanotechnology has evolved into a key field for precise and controlled delivery of various drugs that lack aqueous solubility, have low oral bioavailability and possess pronounced toxicity in their native form. In this review, we discuss various nanoformulations of natural products with favorable ADME properties, and also briefly explore nano-drug delivery to lungs, the primary site of SARS-CoV-2 infection. Natural products are also envisioned to augment nanotechnology-based 1) personnel protective equipment for ex vivo viral inactivation and 2) wearable sensors that perform rapid and non-invasive analysis of volatile organic compounds in exhaled breath of the infected person after therapeutic food consumption.

A mechanism for matrikine regulation in acute inflammatory lung injury

Proline-glycine-proline (PGP) and its acetylated form (Ac-PGP) are neutrophil chemoattractants generated by collagen degradation, and they have been shown to play a role in chronic inflammatory disease. However, the mechanism for matrikine regulation in acute inflammation has not been well established. Here, we show that these peptides are actively transported from the lung by the oligopeptide transporter, PEPT2. Following intratracheal instillation of Ac-PGP in a mouse model, there was a rapid decline in concentration of the labeled peptide in the bronchoalveolar lavage (BAL) over time and redistribution to extrapulmonary sites. In vitro knockdown of the PEPT2 transporter in airway epithelia or use of a competitive inhibitor of PEPT2, cefadroxil, significantly reduced uptake of Ac-PGP. Animals that received intratracheal Ac-PGP plus cefadroxil had higher levels of Ac-PGP in BAL and lung tissue. Utilizing an acute LPS-induced lung injury model, we demonstrate that PEPT2 blockade enhanced pulmonary Ac-PGP levels and lung inflammation. We further validated this effect using clinical samples from patients with acute lung injury in coculture with airway epithelia. This is the first study to our knowledge to determine the in vitro and in vivo significance of active matrikine transport as a mechanism of modulating acute inflammation and to demonstrate that it may serve as a potential therapeutic target.

The Radiolabeling of a Gly-Sar Dipeptide Derivative with Flourine-18 and Its Use as a Potential Peptide Transporter PET Imaging Agent

We have developed a novel fluorine-18 radiotracer, dipeptide 1, radiolabeled in two steps from mesylate 3. The initial radiolabeling is achieved in a short reaction time (10 min) and purified through solid-phase extraction (SPE) with modest radiochemical yields (rcy = 10 ± 2%, n = 5) in excellent radiochemical purity (rcp > 99%, n = 5). The de-protection of the tert-butyloxycarbonyl (Boc) and trityl group was achieved with mild heating under acidic conditions to provide ¹⁸F-tagged dipeptide 1. Preliminary analysis of ¹⁸F-dipeptide 1 was performed to confirm uptake by peptide transporters (PepTs) in human pancreatic carcinoma cell lines Panc1, BxPC3, and ASpc1, which are reported to express the peptide transporter 1 (PepT1). Furthermore, we confirmed in vivo uptake of ¹⁸F-dipeptide tracer 1 using microPET/CT in mice harboring subcutaneous flank Panc1, BxPC3, and Aspc1 tumors. In conclusion, we have established the radiolabeling of dipeptide 1 with fluoride-18, and demonstrated its potential as an imaging agent which may have clinical applications for the diagnosis of pancreatic carcinomas.

Quantification of membrane transporter proteins in human lung and immortalized cell lines using targeted quantitative proteomic analysis by isotope dilution nanoLC-MS/MS

Information is needed on the expression of transporters in lung to inform drug development and therapeutic decisions. Much of the information currently available is from semiquantitative gene expression or immunometric densitometry studies reported in the literature. NanoLC-MS/MS (MRM mode) isotope dilution targeted quantitative proteomics was used here to quantify twelve selected transporters in fresh human lung membrane fraction samples and in the membrane fraction of selected immortalized human lung epithelial cell line samples. Fractionation was undertaken by homogenization in crude membrane lysis buffer followed by differential centrifugation of the homogenate. In lung membranes we found OATPs to be the most highly expressed transporters of those measured, followed by PEPT2 and ABCs (P-gp & BCRP). SLC22A transporters (OCTs 2 & 3 and OCTN1) were also found to be expressed. OATP2A1, also known as the prostaglandin transporter, was the most highly expressed transporter, being low in two subjects who were at least occasional smokers. One subject, a non-smoker, had an OATP2A1 concentration that was 8.4 times higher than the next nearest concentration, which itself was higher than the concentration of any other transporter. OATP2A1 is known, from gene expression and animal functional studies, to be present in lung. These results inform the understanding of xenobiotic disposition in the lung and show the distinct profile of transporters in lung compared to other tissues.

Pulmonary Pharmacokinetics of Colistin following Administration of Dry Powder Aerosols in Rats

Colistin has been administered via nebulization for the treatment of respiratory tract infections. Recently, dry powder inhalation (DPI) has attracted increasing attention. The current study aimed to investigate the pharmacokinetics (PK) of colistin in epithelial lining fluid (ELF) and plasma following DPI and intravenous (i.v.) administration in healthy Sprague-Dawley rats. Rats were given colistin as DPI intratracheally (0.66 and 1.32 mg base/kg of body weight) or i.v. injection (0.66 mg base/kg). Histopathological examination of lung tissue was performed at 24 h. Colistin concentrations in both ELF and plasma were quantified, and a population PK model was developed and compared to a previously published PK model of nebulized colistin in rats. A two-compartment structural model was developed to describe the PK of colistin in both ELF and plasma following pulmonary or i.v. administration. The model-estimated clearance from the central plasma compartment was 0.271 liter/h/kg (standard error [SE] = 2.51%). The transfer of colistin from the ELF compartment to the plasma compartment was best described by a first-order rate constant (clearance of colistin from the ELF compartment to the plasma compartment = 4.03 × 10^-4 liter/h/kg, SE = 15%). DPI appeared to have a higher rate of absorption (time to the maximum concentration in plasma after administration of colistin by DPI, ≤10 min) than nebulization (time to the maximum concentration in plasma after administration of colistin by nebulization, 20 to 30 min), but the systemic bioavailabilities by the two routes of administration were similar (∼46.5%, SE = 8.43%). Histopathological examination revealed no significant differences in inflammation in lung tissues between the two treatments. Our findings suggest that colistin DPI is a promising alternative to nebulization considering the similar PK and safety profiles of the two forms of administration. The PK and histopathological information obtained is critical for the development of optimal aerosolized colistin regimens with activity against lung infections caused by Gram-negative bacteria.

Nicotine transport in lung and non-lung epithelial cells

AIMS

Nicotine is rapidly absorbed from the lung alveoli into systemic circulation during cigarette smoking. However, mechanism underlying nicotine transport in alveolar epithelial cells is not well understood to date. In the present study, we characterized nicotine uptake in lung epithelial cell lines A549 and NCI-H441 and in non-lung epithelial cell lines HepG2 and MCF-7.

MATERIALS AND METHODS

Characteristics of [³H]nicotine uptake was studied using these cell lines.

KEY FINDINGS

Nicotine uptake in A549 cells occurred in a time- and temperature-dependent manner and showed saturation kinetics, with a Km value of 0.31mM. Treatment with some organic cations such as diphenhydramine and pyrilamine inhibited nicotine uptake, whereas treatment with organic cations such as carnitine and tetraethylammonium did not affect nicotine uptake. Extracellular pH markedly affected nicotine uptake, with high nicotine uptake being observed at high pH up to 11.0. Modulation of intracellular pH with ammonium chloride also affected nicotine uptake. Treatment with valinomycin, a potassium ionophore, did not significantly affect nicotine uptake, indicating that nicotine uptake is an electroneutral process. For comparison, we assessed the characteristics of nicotine uptake in another lung epithelial cell line NCI-H441 and in non-lung epithelial cell lines HepG2 and MCF-7. Interestingly, these cell lines showed similar characteristics of nicotine uptake with respect to pH dependency and inhibition by various organic cations.

SIGNIFICANCE

The present findings suggest that a similar or the same pH-dependent transport system is involved in nicotine uptake in these cell lines. A novel molecular mechanism of nicotine transport is proposed.

Oligopeptide Transport in Rat Lung Alveolar Epithelial Cells is Mediated by Pept2

PURPOSE

Studies were conducted in primary cultured rat alveolar epithelial cell monolayers to characterize peptide transporter expression and function.

METHODS

Freshly isolated rat lung alveolar epithelial cells were purified and cultured on permeable support with and without keratinocyte growth factor (KGF). Messenger RNA and protein expression of Pept1 and Pept2 in alveolar epithelial type I- and type II-like cell monolayers (±KGF, resp.) were examined by RT-PCR and Western blotting. ³H-Glycyl-sarcosine (³H-gly-sar) transmonolayer flux and intracellular accumulation were evaluated in both cell types.

RESULTS

RT-PCR showed expression of Pept2, but not Pept1, mRNA in both cell types. Western blot analysis revealed presence of Pept2 protein in type II-like cells, and less in type I-like cells. Bi-directional transmonolayer ³H-gly-sar flux lacked asymmetry in transport in both types of cells. Uptake of ³H-gly-sar from apical fluid of type II-like cells was 7-fold greater than that from basolateral fluid, while no significant differences were observed from apical vs. basolateral fluid of type I-like cells.

CONCLUSIONS

This study confirms the absence of Pept1 from rat lung alveolar epithelium in vitro. Functional Pept2 expression in type II-like cell monolayers suggests its involvement in oligopeptide lung disposition, and offers rationale for therapeutic development of di/tripeptides, peptidomimetics employing pulmonary drug delivery.

Effect of cigarette smoke extract on P-glycoprotein function in primary cultured and newly developed alveolar epithelial cells

The effect of cigarette smoke extract (CSE) on P-glycoprotein (P-gp) function in the distal lung is unclear. In this study, we first examined the expression and function of P-gp and the effect of CSE in rat primary cultured alveolar epithelial cells. The expression of P-gp protein was observed in type I-like cells, but not in type II cells. In type I-like cells, rhodamine 123 (Rho123) accumulation was enhanced by various P-gp inhibitors such as verapamil and cyclosporine A. In addition, the expression of P-gp mRNAs, mdr1a and mdr1b, as well as P-gp activity increased along with the transdifferentiation. When type I-like cells were co-incubated with CSE, P-gp activity was suppressed. Next, we attempted to clarify the effect of CSE on P-gp function in human-derived cultured alveolar epithelial cells. For this purpose, we isolated an A549 clone (A549/P-gp) expressing P-gp, because P-gp expression in native A549 cells was negligible. In A549/P-gp cells, P-gp was functionally expressed, and the inhibitory effect of CSE on P-gp was observed. These results suggested that smoking would directly suppress P-gp activity, and that A549/P-gp cell line should be a useful model to further study the effect of xenobiotics on P-gp function in the alveolar epithelial cells.

Pulmonary Delivery of the Kv1.3-Blocking Peptide HsTX1[R14A] for the Treatment of Autoimmune Diseases

HsTX1[R14A] is a potent and selective Kv1.3 channel blocker peptide with the potential to treat autoimmune diseases. Given the typically poor oral bioavailability of peptides, we evaluated pulmonary administration of HsTX1[R14A] in rats as an alternative route for systemic delivery. Plasma concentrations of HsTX1[R14A] were measured by liquid chromatography coupled with tandem mass spectrometry in rats receiving intratracheal administration of HsTX1[R14A] in solution (1-4 mg/kg) or a mannitol-based powder (1 mg/kg) and compared with plasma concentrations after intravenous administration (2 mg/kg). HsTX1[R14A] stability in rat plasma and lung tissue was also determined. HsTX1[R14A] was more stable in plasma than in lung homogenate, with more than 90% of the HsTX1[R14A] remaining intact after 5 h, compared with 40.5% remaining in lung homogenate. The terminal elimination half-life, total clearance, and volume of distribution of HsTX1[R14A] after intravenous administration were 79.6 ± 6.5 min, 8.3 ± 0.6 mL/min/kg, and 949.8 ± 71.0 mL/kg, respectively (mean ± SD). After intratracheal administration, HsTX1[R14A] in solution and dry powder was absorbed to a similar degree, with absolute bioavailability values of 39.2 ± 5.2% and 44.5 ± 12.5%, respectively. This study demonstrated that pulmonary administration is a promising alternative for systemically delivering HsTX1[R14A] for treating autoimmune diseases.

Functional Expression of PEPT2 in the Human Distal Lung Epithelial Cell Line NCl-H441

PURPOSE

The peptide transporter PEPT2 is expressed in alveolar type II epithelial cells. So far, however, no appropriate alveolar epithelial cell line for studying PEPT2 function has been known. In this study, we examined the functional expression of PEPT2 in the human distal lung epithelial cell line NCl-H441 (H441).

METHODS

Expression of PEPT2 mRNA and protein was examined in H441 cells. Transport function of PEPT2 was studied using glycylsarcosine (Gly-Sar) as a substrate.

RESULTS

Lamellar bodies were well developed in H441 cells and mRNA expression of type II cell markers and PEPT2 increased during time in culture. PEPT2 protein expression was confirmed in H441 cells, but not in A549 cells, by immunostaining and Western blotting. The uptake of Gly-Sar in H441 cells was inhibited by cefadroxil, and the cefadroxil-sensitive uptake was pH-dependent and peaked at pH 6.5. Gly-Sar uptake in H441 cells showed saturation kinetics with a Km value of 112.5 μM. In addition, apical-to-basal, but not basal-to-apical, transport of cephalexin across H441 cell monolayers was sensitive to cefadroxil.

CONCLUSIONS

PEPT2 is functionally expressed in H441 cells, making the cell line a good in vitro model to study PEPT2 function and its regulation in human distal lung.

Nature and uses of fluorescent dyes for drug transporter studies

INTRODUCTION

Drug transporters are now recognized as major players involved in pharmacokinetics and toxicology. Methods for assessing their activity are important to consider, particularly owing to regulatory requirements with respect to inhibition of drug transporter activity and prediction of drug-drug interactions. In this context, the use of fluorescent-dye-based transport assays is likely to deserve attention.

AREAS COVERED

This review provides an overview of the nature of fluorescent dye substrates for ATP-binding cassette and solute carrier drug transporters. Their use for investigating drug transporter activity in cultured cells and clinical hematological samples, drug transporter inhibition, drug transporter imaging and drug transport at the organ level are summarized.

EXPERT OPINION

A wide range of fluorescent dyes is now available for use in various aspects of drug transporter studies. The use of these dyes for transporter analyses may, however, be hampered by classic pitfalls of fluorescence technology, such as quenching. Transporter-independent processes such as passive diffusion of dyes through plasma membrane or dye sequestration into subcellular compartments must also be considered, as well as the redundant handling by various distinct transporters of some fluorescent probes. Finally, standardization of dye-based transport assays remains an important on-going issue.

Biopharmaceutical characterization of nebulized antimicrobial agents in rats: 2. Colistin

The purpose of this study was to investigate the pharmacokinetic properties of colistin following intrapulmonary administration of colistin sulfate in rats. Colistin was infused or delivered in nebulized form at a dose of 0.35 mg/kg of body weight in rats, and plasma drug concentrations were measured for 4 h after administration. Bronchoalveolar lavages (BAL) were also conducted at 0.5, 2, and 4 h after intravenous (i.v.) administration and administration via nebulized drug to estimate epithelial lining fluid (ELF) drug concentrations. Unbound colistin plasma concentrations at distribution equilibrium (2 h postdosing) were almost identical after i.v. infusion and nebulized drug inhalation. ELF drug concentrations were undetectable in BAL samples after i.v. administration, but they were about 1,800 times higher than unbound plasma drug levels at 2 h and 4 h after administration of the nebulized drug. Simultaneous pharmacokinetic modeling of plasma and ELF drug concentrations was performed with a model characterized by a fixed physiological volume of ELF (VELF), a passive diffusion clearance (QELF) between plasma and ELF, and a nonlinear influx transfer from ELF to the central compartment, which was assessed by reducing the nebulized dose of colistin by 10-fold (0.035 mg kg(-1)). The km was estimated to be 133 μg ml(-1), and the Vmax, in-to-Km ratio was equal to 2.5 × 10(-3) liter h(-1) kg(-1), which was 37 times higher than the QELF (6.7 × 10(-5) liter h(-1) kg(-1)). This study showed that with the higher ELF drug concentrations after administration via nebulized aerosol than after intravenous administration, for antibiotics with low permeability such as colistin, nebulization offers a real potential over intravenous administration for the treatment of pulmonary infections.

Peptide transporter isoforms are discriminated by the fluorophore-conjugated dipeptides β-Ala- and d-Ala-Lys-N-7-amino-4-methylcoumarin-3-acetic acid

Peptide transporters of the SLC15 family are classified by structure and function into PEPT1 (low‐affinity/high‐capacity) and PEPT2 (high‐affinity/low‐capacity) isoforms. Despite the differences in kinetics, both transporter isoforms are reckoned to transport essentially all possible di‐ and tripeptides. We here report that the fluorophore‐conjugated dipeptide derivatives β‐Ala‐Lys‐N‐7‐amino‐4‐methylcoumarin‐3‐acetic acid (β‐AK‐AMCA) and d‐Ala‐Lys‐N‐7‐amino‐4‐methylcoumarin‐3‐acetic acid (d‐AK‐AMCA) are transported by distinct PEPT isoforms in a species‐specific manner. Transport of the fluorophore peptides was studied (1) in vitro after heterologous expression in Xenopus oocytes of PEPT1 and PEPT2 isoforms from different vertebrate species and of PEPT1 and PEPT2 transporters from Caenorhabditis elegans by using electrophysiological and fluorescence methods and (2) in vivo in C. elegans by using fluorescence methods. Our results indicate that both substrates are transported by the vertebrate “renal‐type” and the C. elegans “intestinal‐type” peptide transporter only. A systematic analysis among species finds four predicted amino acid residues along the sequence that may account for the substrate uptake differences observed between the vertebrate PEPT1/nematode PEPT2 and the vertebrate PEPT2/nematode PEPT1 subtype. This selectivity on basis of isoforms and species may be helpful in better defining the structure–function determinants of the proteins of the SLC15 family.

Peptide transporters of the SLC15 family can be classified by structure and function into the PEPT1 (low‐affinity/high‐capacity) and PEPT2 (high‐affinity/low‐capacity) phenotype. We found that the fluorophore‐conjugated dipeptide derivatives β‐Ala‐Lys‐N‐7‐amino‐4‐methylcoumarin‐3‐acetic acid (β‐AK‐AMCA) and d‐Ala‐Lys‐N‐7‐amino‐4‐methylcoumarin‐3‐acetic acid (d‐AK‐AMCA) are transported only by distinct PEPT isoforms in a species‐specific manner. This selectivity on basis of isoforms and species should be helpful in further defining the substrate‐binding domain of peptide transporters.

[Expression of PEPT2 mRNA in lung tissue of rats with pulmonary fibrosis]

背景与目的

肺纤维化是肺癌放化疗后的常见病理改变，是阻碍药物转运到肺部的关键因素之一，肽转运载体已经成为合理设计肽和肽类药物的靶标，本研究旨在探讨肽转运载体2（peptide transporter 2, PEPT2）mRNA在肺纤维化大鼠肺组织中的表达。

方法

健康SD大鼠50只，随机分为5组。博莱霉素（bleomycin, BLM）7 d、14 d、28 d组：气管内一次性滴入博莱霉素溶液复制肺纤维化大鼠模型，分别于给药后7 d、14 d和28 d放血处死；生理盐水组滴入等量生理盐水，于14 d放血处死；正常组不做任何处理。各组取肺组织，光镜观察组织病理变化；检测样本羟脯氨酸含量；半定量RT-PCR检测肺组织PEPT2 mRNA表达。

结果

BLM 7 d组大鼠肺组织呈急性炎症性改变，无纤维增生；BLM 14 d组和28 d组大鼠肺组织均有纤维化改变，以28 d组最为明显。BLM 7 d组肺组织羟脯氨酸含量与正常对照组和生理盐水组相比无统计学差异（P > 0.05）；14 d组和28 d组大鼠肺组织羟脯氨酸含量均高于正常对照组和生理盐水组（P < 0.05）。各组肺组织PEPT2 mRNA的相对表达量无统计学差异（P > 0.05）。

结论

PEPT2 mRNA在博莱霉素致肺纤维化大鼠肺组织表达水平无明显变化，PEPT2可能是设计肺纤维化的新型肽类药物靶标之一。

Transcriptional down-regulation of suppressor of cytokine signaling (SOCS)-3 in chronic obstructive pulmonary disease

BACKGROUND

Tobacco is a leading environmental factor in the initiation of respiratory diseases and causes chronic obstructive pulmonary disease (COPD). Suppressor of cytokine signaling (SOCS) family members are involved in the pathogenesis of many inflammatory diseases and SOCS-3 has been shown to play an important role in the regulation, onset and maintenance of airway allergic inflammation indicating that SOCS-3 displays a potential therapeutic target for anti-inflammatory respiratory drugs development. Since chronic obstructive pulmonary disease (COPD) is also characterized by inflammatory changes and airflow limitation, the present study assessed the transcriptional expression of SOCS-3 in COPD.

METHODS

Real-time PCR was performed to assess quantitative changes in bronchial biopsies of COPD patients in comparison to unaffected controls.

RESULTS

SOCS-3 was significantly down-regulated in COPD at the transcriptional level while SOCS-4 and SOCS-5 displayed no change.

CONCLUSIONS

It can be concluded that the presently observed inhibition of SOCS-3 mRNA expression may be related to the dysbalance of cytokine signaling observed in COPD.

Mechanisms of absorption and elimination of drugs administered by inhalation

Pulmonary drug delivery is an effective route for local or systemic drug administration. However, compared with other routes of administration, there is a scarcity of information on how drugs are absorbed from the lung. The different cell composition lining the airways and alveoli makes this task extremely complicated. Lung cell lines and primary culture cells are useful in studying the absorption mechanisms. However, it is imperative that these cell cultures express essential features required to study these mechanisms such as intact tight junctions and transporters. In vivo, the drug has to face defensive physical and immunological barriers such as mucociliary clearance and alveolar macrophages. Knowledge of the physicochemical properties of the drug and aerosol formulation is required. All of these factors interact together leading to either successful drug deposition followed by absorption or drug elimination. These aspects concerning drug transport in the lung are addressed in this review.

Passive lung-targeted drug delivery systems via intravenous administration

The treatment of lung diseases including lung cancer and tuberculosis is one of the most challenging problems in clinical practice, because the conventional drug delivery systems cannot deliver drug effectively to the lung, which result in low therapeutic effect. Therefore, lung-targeted drug delivery systems (LTDDS) that can deliver drug to the lung in an effective way to increase drug concentration in lung tissue and reduce drug distribution in other organs and tissues become an ideal strategy to treat lung diseases. The LTDDS mainly include microparticles (microspheres and microencapsules), liposomes and nanoparticles via intravenous administration, and dry powder carriers and nebulized suspensions via pulmonary inhalation. As lungs possess the large absorptive surface area, the low thickness of the epithelial barrier and good blood supply, pulmonary inhalation has received great attention. Intravenous route is the commonly practiced method for administration of larger doses of drugs into the body. Numerous drugs can be delivered directly into general circulation by avoiding their first-pass metabolism and have potential to transport drugs to the lung via intravenous administration. This present article reviews the development, evaluation and application of LTDDS via intravenous administration for the treatment of lung diseases reported in the past decades.

Inhaled chemotherapy in lung cancer: future concept of nanomedicine

Regional chemotherapy was first used for lung cancer 30 years ago. Since then, new methods of drug delivery and pharmaceuticals have been investigated in vitro, and in animals and humans. An extensive review of drug delivery systems, pharmaceuticals, patient monitoring, methods of enhancing inhaled drug deposition, safety and efficacy, and also additional applications of inhaled chemotherapy and its advantages and disadvantages are presented. Regional chemotherapy to the lung parenchyma for lung cancer is feasible and efficient. Safety depends on the chemotherapy agent delivered to the lungs and is dose-dependent and time-dependent. Further evaluation is needed to provide data regarding early lung cancer stages, and whether regional chemotherapy can be used as neoadjuvant or adjuvant treatment. Finally, inhaled chemotherapy could one day be administered at home with fewer systemic adverse effects.

Pulmonary drug delivery strategies: A concise, systematic review

Because of limitations associated with the conventional treatment of various chronic diseases a growing attention has been given to the development of targeted drug delivery systems. Pulmonary route of drug delivery gaining much importance in the present day research field as it enables to target the drug delivery directly to lung both for local and systemic treatment. Over the last 2 decades, the systemic absorption of a broad range of therapeutics after pulmonary application has been demonstrated in animals as well as in humans. This review was prepared with an aim to discuss the technical, physiological, and efficacy aspects of the novel pulmonary route of drug targeting. The review also focuses on the mechanisms of pulmonary drug administration along with compatibility of the excipients employed, devices used, and techniques of particulate dosage production. This review was prepared based on the method of extensive literature survey on the topics covering all the aspects discussed in the present subject. Hence, the better understanding of complexes and challenges facing the development of pulmonary drug delivery system offer an opportunity to the pharmaceutical scientist in minimizing the clinical and technical gaps.

Spatial expression and functionality of drug transporters in the intact lung: objectives for further research

This commentary provides a background appraising evidence in the intact lung on the spatial expression of drug transporters and, where available, evidence in the intact lung of the impact, or otherwise, that such transporters can have upon pulmonary drug absorption and disposition. Ultimately drug discovery and development scientists will wish to identify in a 'pulmonary' context the effect of disease upon transporter function, the potential for drug transporters to contribute to drug-drug interactions and to inter-individual variation in drug handling and response. The rate and extent of lung epithelial permeation of drugs involve an interplay between the dose and the deposition site of drug within the lung and physiological variables operational at the epithelial-luminal interface. Amongst the latter variables is the potential impact of active transporter processes which may well display regio-selective characteristics along the epithelial tract. In pulmonary tissues the spatial pattern of drug transporter expression is generally poorly defined and the functional significance of transporters within the intact lung is explored in only a limited manner. Active transporters in the lung epithelium may affect airway residence times of drug, modulate access of drug to intracellular targets and to submucosal lung tissue, and potentially influence airway to systemic drug absorption profiles. Transporters in the lung tissue may also have the capacity to mediate uptake of drug from the systemic circulation resulting in drug accumulation in the lung. Transporters have physiological roles and new drug candidates while not necessarily serving as transport substrates may modulate transporter activity and hence physiology. The commentary highlights a series of recommendations for further work in pulmonary drug transporter research.

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.

Functional expression of SLC15 peptide transporters in rat thyroid follicular cells

Peptide transport and expression of SoLute Carrier 15 (SLC15) peptide transporters was assessed in rat thyroid tissue and a rat thyroid cell line (PC Cl3 cells). Peptide transport was studied by monitoring the uptake of the fluorophore-conjugated dipeptide beta-Ala-Lys-N(epsilon)-7-amino-4-methyl-coumarin-3-acetic acid (Ala-Lys-AMCA). Expression of SLC15-specific mRNA transcripts was analyzed by RT-PCR. Of the two SLC15 transporters expressed in thyroid follicular cells, namely PEPT2 (SLC15A2) and PHT1 (SLC15A4), only PEPT2 was involved in peptide transport at the plasma membrane, with PHT1 most likely being intracellular. Interestingly, at the mRNA level PEPT2 was up-regulated under TSH stimulation. These findings represent the first evidence that peptide transport occurs in thyroid follicular cells. SLC15 transporters could participate to recycling of peptides derived from extracellular and lysosomal thyroglobulin proteolysis, both essential steps for thyroid hormone synthesis.

Loss of the apical V-ATPase a-subunit VHA-6 prevents acidification of the intestinal lumen during a rhythmic behavior in C. elegans

In Caenorhabditis elegans, oscillations of intestinal pH contribute to the rhythmic defecation behavior, but the acid-base transport mechanisms that facilitate proton movement are not well understood. Here, we demonstrate that VHA-6, an intestine-specific a-subunit of the H(+)-K(+)-ATPase complex (V-ATPase), resides in the apical membrane of the intestinal epithelial cells and is required for luminal acidification. Disruption of the vha-6 gene led to early developmental arrest; the arrest phenotype could be complemented by expression of a fluorescently labeled vha-6 transgene. To study the contribution of vha-6 to pH homeostasis in larval worms, we used a partial reduction of function through postembryonic single-generation RNA interference. We demonstrate that the inability to fully acidify the intestinal lumen coincides with a defect in pH recovery of the intestinal epithelial cells, suggesting that VHA-6 is essential for proton pumping following defecation. Moreover, intestinal dipeptide accumulation and fat storage are compromised by the loss of VHA-6, suggesting that luminal acidification promotes nutrient uptake in worms, as well as in mammals. Since acidified intracellular vesicles and autofluorescent storage granules are indistinguishable between the vha-6 mutant and controls, it is likely that the nutrient-restricted phenotype is due to a loss of plasma membrane V-ATPase activity specifically. These data establish a simple genetic model for proton pump-driven acidification. Since defecation occurs at 45-s intervals in worms, this model represents an opportunity to study acute regulation of V-ATPase activity on a short time scale and may be useful in the study of alternative treatments for acid-peptic disorders.

The role of transporters in the pharmacokinetics of orally administered drugs

Drug transporters are recognized as key players in the processes of drug absorption, distribution, metabolism, and elimination. The localization of uptake and efflux transporters in organs responsible for drug biotransformation and excretion gives transporter proteins a unique gatekeeper function in controlling drug access to metabolizing enzymes and excretory pathways. This review seeks to discuss the influence intestinal and hepatic drug transporters have on pharmacokinetic parameters, including bioavailability, exposure, clearance, volume of distribution, and half-life, for orally dosed drugs. This review also describes in detail the Biopharmaceutics Drug Disposition Classification System (BDDCS) and explains how many of the effects drug transporters exert on oral drug pharmacokinetic parameters can be predicted by this classification scheme.

Bacterial peptide recognition and immune activation facilitated by human peptide transporter PEPT2

Microbial detection requires the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs) that are distributed on the cell surface and within the cytosol. The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family functions as an intracellular PRR that triggers the innate immune response. The mechanism by which PAMPs enter the cytosol to interact with NLRs, particularly muropeptides derived from the bacterial proteoglycan cell wall, is poorly understood. PEPT2 is a proton-dependent transporter that mediates the active translocation of di- and tripeptides across epithelial tissues, including the lung. Using computational tools, we initially established that bacterial dipeptides, particularly gamma-D-glutamyl-meso-diaminopimelic acid (gamma-iE-DAP), are suitable substrates for PEPT2. We then determined in primary cultures of human upper airway epithelia and transiently transfected CHO-PEPT2 cell lines that gamma-iE-DAP uptake was mediated by PEPT2 with an affinity constant of approximately 193 microM, whereas muramyl dipeptide was not transported. Exposure to gamma-iE-DAP at the apical surface of differentiated, polarized cultures resulted in activation of the innate immune response in an NOD1- and RIP2-dependent manner, resulting in release of IL-6 and IL-8. Based on these findings we report that PEPT2 plays a vital role in microbial recognition by NLR proteins, particularly with regard to airborne pathogens, thereby participating in host defense in the lung.

hPEPT1 is responsible for uptake and transport of Gly-Sar in the human bronchial airway epithelial cell-line Calu-3

The purpose of this work was to investigate the apical uptake and transepithelial transport of Gly-Sar along with the expression of the di-/tripeptide transporters hPEPT1 and hPEPT2 in human Calu-3 bronchial epithelial cells. The apical Gly-Sar uptake rate in Calu-3 cells followed Michaelis-Menten kinetics with a Km value of 1.3 +/- 0.3 mM and a Vmax value of 0.60 +/- 0.06 nmol cm(-2) min(-1). Transepithelial apical to basolateral transport of 50 microM [3H]-labelled Gly-Sar across the Calu-3 cell monolayer was pH-dependent. The Gly-Sar flux was significantly reduced in the presence of delta-aminolevulinic acid (2.5 mM), cephalexin (25 mM), and captopril (25 mM; p < 0.05, n = 3). Reverse transcriptase polymerase chain reaction (RT-PCR) revealed the presence of both hPEPT1 and hPEPT2 mRNA in the Calu-3 cells. These findings were confirmed in healthy human bronchial cDNA. Restriction-endonuclease analysis identified hPEPT2 in Calu-3 cells to be the hPEPT2*1 haplotype. Western blotting demonstrated expression of the hPEPT1 protein (approximately 80 kDa), and the immunolabel was mainly localized in the apical membrane as judged by immunolocalization studies using confocal laser scanning microscopy (CLSM). This work presents for the first time hPEPT1 and hPEPT2*1 expression in human Calu-3 cells. Surprisingly, the results indicate that Gly-Sar uptake and transport in Calu-3 cells are hPEPT1-mediated rather than hPEPT2-mediated.

Analysis of airway secretions in a model of sulfur dioxide induced chronic obstructive pulmonary disease (COPD)

Hypersecretion and chronic phlegm are major symptoms of chronic obstructive pulmonary disease (COPD) but animal models of COPD with a defined functional hypersecretion have not been established so far. To identify an animal model of combined morphological signs of airway inflammation and functional hypersecretion, rats were continuously exposed to different levels of sulfur dioxide (SO2, 5 ppm, 10 ppm, 20 ppm, 40 ppm, 80 ppm) for 3 (short-term) or 20–25 (long-term) days. Histology revealed a dose-dependent increase in edema formation and inflammatory cell infiltration in short-term-exposed animals. The submucosal edema was replaced by fibrosis after long-term-exposure. The basal secretory activity was only significantly increased in the 20 ppm group. Also, stimulated secretion was significantly increased only after exposure to 20 ppm. BrdU-assays and AgNOR-analysis demonstrated cellular metaplasia and glandular hypertrophy rather than hyperplasia as the underlying morphological correlate of the hypersecretion.

In summary, SO2-exposure can lead to characteristic airway remodeling and changes in mucus secretion in rats. As only long-term exposure to 20 ppm leads to a combination of hypersecretion and airway inflammation, only this mode of exposure should be used to mimic human COPD. Concentrations less or higher than 20 ppm or short term exposure do not induce the respiratory symptom of hypersecretion. The present model may be used to characterize the effects of new compounds on mucus secretion in the background of experimental COPD.

Novel strategies of aerosolic pharmacotherapy

The pulmonary administration of drugs plays a crucial role in the management of various respiratory and systemic diseases. While the cellular properties of airway epithelial cells offer a great potential to deliver drugs into the lungs or the circulation, only little is known about the exact transport pathways. Recently, the high-affinity proton-coupled drug and peptide transporter PEPT2 was identified in the human respiratory tract. The expression of transporter mRNA and protein was localized to the airway epithelium and alveolar type II pneumocytes. In addition, transport studies revealed transporter-mediated uptake of substrates into epithelial cells indicating that the transporter is the molecular basis for the transport of peptides and peptidomimetic drugs in pulmonary epithelial cells. Since genotype analysis revealed no significant differences amongst different transporter genotypes concerning expression and function, the transporter displays an interesting novel target for pulmonary delivery of drugs.

Asthma and COPD

The two obstructive airway diseases bronchial asthma and chronic obstructive pulmonary disease (COPD) represent major global causes of disability and death, and COPD is estimated to become the third most common cause of death by 2020. The structural and pathophysiologic findings in both diseases appear to be easily differentiated in the extremes of clinical presentation. However, a significant overlap may exist in individual patients regarding features such as airway wall thickening on computer tomography or reversibility and airway hyperresponsiveness in lung function tests. Airway inflammation differs between the two diseases. In bronchial asthma, airway inflammation is characterized in most cases by an increased number of activated T-lymphocytes, particularly CD4+ Th2 cells, and sometimes eosinophils and mast cells. The most notable difference of chronic severe asthma compared with mild to moderate asthma is an increased number of neutrophils. In stable COPD, airway inflammation is characterized by an increased number of T-lymphocytes, particularly CD8+ T cells, macrophages and neutrophils. With the progression of the disease severity, macrophage and neutrophil numbers increase. Although there may be a partial overlap between asthma and COPD in some patients, the differences in functional, structural and pharmacological features clearly demonstrate the consensus that asthma and COPD are different diseases along all their stages of severity.

Novel concepts of neuropeptide-based drug therapy: vasoactive intestinal polypeptide and its receptors

Chronic inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD) are major contributors to the global burden of disease. Although inflammatory cells play the central role in the pathogenesis of the diseases, recent observations indicate that also resident respiratory cells represent important targets for pulmonary drug development. Especially targeting airway neuromediators offers a possible mechanism by which respiratory diseases may be treated in the future. Among numerous peptide mediators such as tachykinins, calcitonin gene-related peptide, neurotrophins or opioids, vasoactive intestinal polypeptide (VIP) is one of the most abundant molecules found in the respiratory tract. In human airways, it influences many respiratory functions via the receptors VPAC1, VPAC2 and PAC1. VIP-expressing nerve fibers are present in the tracheobronchial smooth muscle layer, submucosal glands and in the walls of pulmonary and bronchial arteries and veins. Next to its strong bronchodilator effects, VIP potently relaxes pulmonary vessels, and plays a pivotal role in the mediation of immune mechanisms. A therapy utilizing the respiratory effects of VIP would offer potential benefits in the treatment of obstructive and inflammatory diseases and long acting VIP-based synthetic non-peptide compounds may represent a novel target for drug development.

Chronic cough due to occupational factors

Within the large variety of subtypes of chronic cough, either defined by their clinical or pathogenetic causes, occupational chronic cough may be regarded as one of the most preventable forms of the disease. Next to obstructive airway diseases such as asthma or chronic obstructive pulmonary disease, which are sometimes concomitant with chronic cough, this chronic airway disease gains importance in the field of occupational medicine since classic fiber-related occupational airway diseases will decrease in the future.

Apart from acute accidents and incidental exposures which may lead to an acute form of cough, there are numerous sources for the development of chronic cough within the workplace. Over the last years, a large number of studies has focused on occupational causes of respiratory diseases and it has emerged that chronic cough is one of the most prevalent work-related airway diseases. Best-known examples of occupations related to the development of cough are coal miners, hard-rock miners, tunnel workers, or concrete manufacturing workers.

As chronic cough is often based on a variety of non-occupational factors such as tobacco smoke, a distinct separation into either occupational or personally -evoked can be difficult. However, revealing the occupational contribution to chronic cough and to the symptom cough in general, which is the commonest cause for the consultation of a physician, can significantly lead to a reduction of the socioeconomic burden of the disease.

Study of the mechanisms of uptake of 5-aminolevulinic acid derivatives by PEPT1 and PEPT2 transporters as a tool to improve photodynamic therapy of tumours

Endogenous porphyrin accumulation after administration of 5-aminolevulinic acid is employed in photodynamic therapy of tumours. Due to its low membrane permeability, esterified 5-aminolevulinic acid derivatives less hydrophilic than the parental compound are under investigation. Knowledge of the mechanisms of 5-aminolevulinic acid derivatives uptake into target cells is essential to understand and improve photodynamic therapy and useful in the design of new derivatives with better affinity and with higher selectivity for tumour cells in specific tissues. The aim of this work was to assess the interaction of 5-aminolevulinic acid derivatives with the intestinal PEPT1 and renal transporter PEPT2 expressed in Pichia pastoris yeasts. We found that Undecanoyl, Hexyl, Methyl and 2-(hydroxymethyl)tetrahydropyranyl 5-aminolevulinic acid esters and the dendron 3m-ALA inhibited (14)C-5-aminolevulinic acid uptake by PEPT2. However, only the Undecanoyl ester inhibited 5-aminolevulinic acid uptake by PEPT1. We have also found through a new developed colorimetric method, that Hexyl and 2-(hydroxymethyl)tetrahydropyranyl 5-aminolevulinic acid esters display more affinity than 5-aminolevulinic acid for PEPT2 whereas none of the compounds surpass 5-aminolevulinic acid affinity for PEPT1. In addition, the Undecanoyl ester binds with high affinity to the membranes of PEPT2 and PEPT1-expressing yeasts and to the control yeasts. The main finding of this work was that some derivatives have the potential to improve 5-aminolevulinic acid-based photodynamic therapy by increased efficiency of transport into cells expressing PEPT2 such as kidney, mammary gland, brain or lung whereas in tissues expressing exclusively PEPT1 the parent 5-aminolevulinic acid remains the compound of choice.

The Lung, an Organ for Absorption?

This review summarizes information concerning the mechanisms of absorption of substances across the pulmonary epithelium. Inhalation is now increasingly used as a route of administration, although the scientific understanding of these mechanisms is rather limited. The aim of this study is to draw attention to these questions.

Cell culture models of the respiratory tract relevant to pulmonary drug delivery

The respiratory tract holds promise as an alternative site of drug delivery due to fast absorption and rapid onset of drug action, with avoidance of hepatic and intestinal first-pass metabolism as an additional benefit compared to oral drug delivery. At present, the pharmaceutical industry increasingly relies on appropriate in vitro models for the faster evaluation of drug absorption and metabolism as an alternative to animal testing. This article reviews the various existing cell culture systems that may be applied as in vitro models of the human air-blood barrier, for instance, in order to enable the screening of large numbers of new drug candidates at low cost with high reliability and within a short time span. Apart from such screening, cell culture-based in vitro systems may also contribute to improve our understanding of the mechanisms of drug transport across such epithelial tissues, and the mechanisms of action how advanced drug carriers, such as nanoparticles or liposomes, can help to overcome these barriers. After all, the increasing use and acceptance of such in vitro models may lead to a significant acceleration of the drug development process by facilitating the progress into clinical studies and product registration.

Hypothyroidism induces expression of the peptide transporter PEPT2

The kidney is a target organ for thyroid hormone action and a variety of renal transport processes are altered in response to impaired thyroid functions. To investigate the effect of thyroid hormone on the expression of the renal proximal tubular high-affinity-type H+-peptide cotransporter (PEPT2) in rats, hypothyroidism was induced in animals by administration of methimazole (0.05%) via drinking water. After 7 weeks of treatment, hypothyroidism was confirmed by determining serum free T3 and free T4 concentrations. Northern blotting was used to examine the expression of PEPT2 mRNA in kidney tissues from hypothyroid rats compared to control rats. Hypothyroidism resulted in an increased level of total renal PEPT2 mRNA (121.1±3.3% vs. control 100±2.8%; p=0.008). The mRNA results were confirmed by immuno-blotting, which demonstrated significantly increased protein levels (162% vs. control 100%; p<0.01). Immunohistochemistry also revealed increased PEPT2 protein levels in the proximal tubules of treated compared to non-treated rats. In summary, PEPT2 is the first proximal tubule transporter protein that shows increased expression in states of hypothyreosis. As PEPT2 reabsorbs filtered di- and tripeptides and peptide-like drugs, the present findings may have important implications in nutritional amino acid homeostasis and for drug dynamics in states of altered thyroid function.

Comparison of human and monkey peptide transporters: PEPT1 and PEPT2

Human proton-dependent peptide transporters, PEPT1 and PEPT2, mediate the cellular uptake of di- and tripeptides as well as a variety of drug molecules. Although PEPT1 and PEPT2 have been cloned from many species, there are no data available for monkey, an important pharmacological and preclinical species in drug development. In this study, it was first verified that monkey intestine transports a model dipeptide, Gly-Sar, in a proton-dependent manner (0.30 +/- 0.05 pmol cm(-2) s(-1) at pH 6.0 and 0.10 +/- 0.03 pmol cm(-2) s(-1) at pH 7.4) in the absorptive direction, presumably by monkey PEPT1. RT-PCR and rapid amplification of cDNA ends (RACE) were then used to clone monkey PEPT1 and PEPT2. Monkey PEPT1 (2127 bp and 708 amino acids) was found to be >94 and > 92% identical to human PEPT1 at the cDNA and amino acid level, respectively. Monkey PEPT2 (2190 bp and 729 amino acids) was found to be > 97% identical to human PEPT2 at both the cDNA and amino acid levels. Functional comparison of human and monkey peptide transporters expressed in HeLa cells suggested that functionalities of PEPT1 and PEPT2 were largely conserved in terms of Gly-Sar uptake kinetics and inhibitor specificity (for most tested substrates). Finally, Northern and RT-PCR analyses revealed some differences in tissue mRNA levels of peptide transporters between human and monkey.

Functional Characterization of the Peptide Transporter PEPT2 in Primary Cultures of Human Upper Airway Epithelium

This study characterizes the expression and function of the peptide transporter hPepT2 (SLC15A2) in differentiated primary cultures of human upper airway lung epithelia obtained from six human donors. Genotype analysis of a SNP in exon 15 of hPepT2 genotypes in six donors revealed an expected distribution of the two main variants present at similar frequency (two AA homozygotes, two BB homozygotes, and two AB heterozygotes). Real-time PCR analysis of the hPepT2 mRNA message revealed no significant differences among genotypes. hPEPT2 was expressed on the apical membrane in all donor specimens, demonstrated by cell surface biotinylation and Western analysis (104 kD). We then compared transepithelial transport of the prototypical substrate (3)H-glycylsarcosine in all donor cultures in the absence and presence of known inhibitors of hPEPT2 to ascertain the phenotype of functionally expressed hPepT2 in the upper airway epithelium. An array of inhibitors included dipeptides, beta-lactam antibiotics, bestatin, and ACE inhibitors. hPEPT2 exhibited saturable Michaelis-Menten-type kinetic parameters for GlySar, corroborating previously reported values for K(T) and J(max). Donor-to-donor variation of transport for different substrates did not correlate with hPepT2 haplotypes in this sample cohort. These findings demonstrate functional hPEPT2 transporter expression in primary cultures of human lung epithelial cells. hPEPT2-mediated transport could serve as a strategy for noninvasive systemic delivery of peptides and peptidomimetics drugs.

Transporter-mediated drug delivery: recent progress and experimental approaches

A comprehensive list of drug transporters has recently become available as a result of extensive genome analysis, as well as membrane physiology and molecular biology studies. This review covers recent progress in identification and characterization of drug transporters, illustrative cases of successful drug delivery to, or exclusion from, target organs via transporters, and novel experimental approaches to therapeutics using heterologously transduced transporters in tissues. We aim to provide clues that could lead to efficient strategies for the use of transporters to deliver drugs and/or to optimize lead compounds.

Molecular mechanisms of severe acute respiratory syndrome (SARS)

Severe acute respiratory syndrome (SARS) is a new infectious disease caused by a novel coronavirus that leads to deleterious pulmonary pathological features. Due to its high morbidity and mortality and widespread occurrence, SARS has evolved as an important respiratory disease which may be encountered everywhere in the world. The virus was identified as the causative agent of SARS due to the efforts of a WHO-led laboratory network. The potential mutability of the SARS-CoV genome may lead to new SARS outbreaks and several regions of the viral genomes open reading frames have been identified which may contribute to the severe virulence of the virus. With regard to the pathogenesis of SARS, several mechanisms involving both direct effects on target cells and indirect effects via the immune system may exist. Vaccination would offer the most attractive approach to prevent new epidemics of SARS, but the development of vaccines is difficult due to missing data on the role of immune system-virus interactions and the potential mutability of the virus. Even in a situation of no new infections, SARS remains a major health hazard, as new epidemics may arise. Therefore, further experimental and clinical research is required to control the disease.

Effects of alpha calcitonin gene-related peptide in human bronchial smooth muscle and pulmonary artery

Although airway and pulmonary vessel tone are regulated predominantly by cholinergic and adrenergic impulses, biologically active peptides such as calcitonin gene-related peptide (CGRP) may significantly influence human smooth muscle tone in normal and pathophysiological states. In the present study, the expression of CGRP and its receptor CGRPR-1 and the biological effect of the peptide were investigated in human airways and pulmonary arteries. Immunohistochemistry revealed the presence of CGRP in human airway nerves and neuro-epithelial cells, whereas the receptor was found in epithelial cells and smooth muscle myocytes of the bronchi and in pulmonary artery endothelium. On precontracted bronchi (3-4 mm in diameter) alpha-CGRP (0.01-10 nM) caused a concentration-dependent contraction on epithelium-denuded bronchi, whereas no significant effect was recorded in bronchi with intact epithelium. In pulmonary arteries (2-6 mm in diameter), alpha-CGRP caused a concentration-dependent relaxation of endothelium intact and denuded vessels. Pre-treatment with indomethacin, but not with l-NAME, prevented the relaxation induced by alpha-CGRP in pulmonary arteries suggesting that prostaglandins but not nitric oxide (NO) are involved in the intracellular signal transduction pathway. The effects induced by alpha-CGRP in bronchi and vessels were prevented by application of the antagonist CGRP((8-37)). In summary, the present studies examined the biological function of CGRP in human airways and demonstrated a constrictory effect of CGRP only in epithelium-denuded airway smooth muscle indicating an alteration of CGRP airway effects in respiratory tract pathological states with damaged epithelium such as chronic obstructive pulmonary disease or bronchial asthma.