DSPE-PEG polymers for improving pulmonary absorption of poorly absorbed macromolecules in rats and relative mechanism

OBJECTIVE

This study aims to investigate the potential of DSPE-PEG polymers (DSPE-PEG-OH and DSPE-PEG-SH) on improving absorption of poorly absorbable macromolecules via intrapulmonary administration and underlying mechanism.

METHODS

In situ pulmonary absorption experiments were performed to investigate the absorption of model compounds after intrapulmonary administration to rats. The local membrane damage induced by these DSPE-PEG polymers were evaluated based on morphological observation of lung tissues and measurement of biological toxic markers in bronchoalveolar lavage fluid (BALF) postintrapulmonary delivery of DSPE-PEG polymers to rats. The underlying enhancement mechanism of these polymers was explored by investigating their effects on the pulmonary membrane fluidity and gene expression of tight junction associated proteins with fluorescence polarization and western blotting, respectively.

RESULTS

Intrapulmonary delivery of these DSPE-PEG polymers significantly enhanced absorptions of poorly absorbed model drugs and did not induce serious damage to the pulmonary membranes of rats. Mechanistic studies demonstrated unaffected pulmonary membrane fluidity and up-regulated expression levels of tight junction-associated proteins by DSPE-PEG polymers, thus indicating that paracellular pathways might be included in the underlying mechanisms by which DSPE-PEG polymers exerted their enhancing actions on drug absorption.

CONCLUSIONS

These findings suggested that these DSPE-PEG polymers are potential for promoting absorptions of poorly absorbable macromolecules with no evidence of damage to the local pulmonary membranes of rats.Novelty statementIn this study, DSPE-PEG-OH and DSPE-PEG-SH polymers, two DSPE-PEG2000 conjugates with different terminal groups demonstrated significant promoting effects on the absorption of poorly absorbed macromolecular drugs after intrapulmonary delivery to rats, and did not induce serious damage to the pulmonary membranes of rats. These DSPE-PEG polymers could statistically downregulate expression levels of tight junction-associated proteins (ZO-1 and occludin), indicating the underlying mechanism by which these polymers exerted their absorption enhancing actions through pulmonary epithelial paracellular pathways. Thus, this study exhibited prospective potential of these DSPE-PEG polymers in developing into dosage forms with the aim to improve the poor bioavailability of some poorly absorbed macromolecular drugs.

Caproyl-Modified G2 PAMAM Dendrimer (G2-AC) Nanocomplexes Increases the Pulmonary Absorption of Insulin

We aimed to investigate the absorption-enhancing effect (AEE) of caproyl-modified G2 PAMAM dendrimer (G2-AC) on peptide and protein drugs via the pulmonary route. In this study, G2 PAMAM dendrimer conjugates modified with caproic acid was synthesized, the pulmonary absorption of insulin as models with or without G2-AC were evaluated. The results indicated that G2-AC6 exhibited a greatest AEE for insulin in various caproylation levels of G2-AC. G2-AC6 could significantly enhance the absorption of insulin, and the AEE of G2-AC6 was concentration-dependent. In toxicity tests, G2-AC6 displayed no measurable cytotoxicity to the pulmonary membranes over a concentration range from 0.1% (w/v) to 1.0% (w/v). Measurements of the TEER and permeability showed that G2-AC6 significantly reduced the TEER value of CF and increased its P_app value. The results suggested that G2-AC6 could cross epithelial cells by means of a combination of paracellular and transcellular pathways. These findings suggested G2-AC6 at lower concentrations (below 1.0%, w/v) might be promising absorption enhancers for increasing the pulmonary absorption of peptide and protein drugs.

Pulmonary Delivery of Triptorelin Loaded in Pluronic Based Nanomicelles in Rat Model

INTRODUCTION

Triptorelin, the synthetic analog of gonadotrophin-releasing hormone, is used for the treatment of sex hormone dependent diseases via parenteral administration. The aim of the present study was to investigate the possibility of triptorelin pulmonary delivery and preparation of a pulmonary nanocarrier delivery system for it.

METHODS

Triptorelin was loaded in Pluronic-F127 grafted poly (methyl vinyl ether-alt-maleic acid) nanomicelles by direct dissolution method. Effects of the processing variables including: drug/polymer ratio, temperature, stirring rate and time on the physicochemical properties of nanomicelles including zeta potential, particle size, drug entrapment efficiency and release profiles of triptorelin loaded nanomicelles were evaluated. For animal studies 24 Wistar rats were separated into four groups of six. Group 1 received blank nanomicelles, groups 2, 3 and 4 were treated with a single dose of 250 µg.kg-1 of triptorelin solution subcutaneously (sc), pulmonary spraying of triptorelin solution (250 µg.kg-1) and pulmonary spraying of triptorelin nanomicelles (250 µg.kg-1), respectively by microsprayer.

RESULTS

The optimized micelles had particle size of 87.35 nm, zeta potential of -12.8 mV, entrapment efficiency of 84.36% and release efficiency of 65%. The area under the blood testosterone levels increment differed significantly (p<0.05) between pulmonary triptorelin nanomicelles and drug solution. The pharmacological activity of the simple solution was 59.38%, while it was 80.18% for the nanomicelles relative to sc route of administration with prolonged residence time.

CONCLUSION

The results of this study show that not only triptorelin is absorbable from the lungs but also nanomicelles can significantly enhance its pulmonary absorption compared to its simple solution.

The Differential Absorption of a Series of P-Glycoprotein Substrates in Isolated Perfused Lungs from Mdr1a/1b Genetic Knockout Mice can be Attributed to Distinct Physico-Chemical Properties: an Insight into Predicting Transporter-Mediated, Pulmonary Specific Disposition

PURPOSE

To examine if pulmonary P-glycoprotein (P-gp) is functional in an intact lung; impeding the pulmonary absorption and increasing lung retention of P-gp substrates administered into the airways. Using calculated physico-chemical properties alone build a predictive Quantitative Structure-Activity Relationship (QSAR) model distinguishing whether a substrate's pulmonary absorption would be limited by P-gp or not.

METHODS

A panel of 18 P-gp substrates were administered into the airways of an isolated perfused mouse lung (IPML) model derived from Mdr1a/Mdr1b knockout mice. Parallel intestinal absorption studies were performed. Substrate physico-chemical profiling was undertaken. Using multivariate analysis a QSAR model was established.

RESULTS

A subset of P-gp substrates (10/18) displayed pulmonary kinetics influenced by lung P-gp. These substrates possessed distinct physico-chemical properties to those P-gp substrates unaffected by P-gp (8/18). Differential outcomes were not related to different intrinsic P-gp transporter kinetics. In the lung, in contrast to intestine, a higher degree of non-polar character is required of a P-gp substrate before the net effects of efflux become evident. The QSAR predictive model was applied to 129 substrates including eight marketed inhaled drugs, all these inhaled drugs were predicted to display P-gp dependent pulmonary disposition.

CONCLUSIONS

Lung P-gp can affect the pulmonary kinetics of a subset of P-gp substrates. Physico-chemical relationships determining the significance of P-gp to absorption in the lung are different to those operative in the intestine. Our QSAR framework may assist profiling of inhaled drug discovery candidates that are also P-gp substrates. The potential for P-gp mediated pulmonary disposition exists in the clinic.

Aerosolized liposomes with dipalmitoyl phosphatidylcholine enhance pulmonary absorption of encapsulated insulin compared with co-administered insulin

OBJECTIVE

We have previously shown that aerosolized liposomes with dipalmitoyl phosphatidylcholine (DPPC) enhance the pulmonary absorption of encapsulated insulin. In this study, we aimed to compare insulin encapsulated into the liposomes versus co-administration of empty liposomes and unencapsulated free insulin, where the DPCC liposomes would serve as absorption enhancer.

SIGNIFICANCE

The present study provides the useful information for development of noninvasive treatment of diabetes.

METHODS

Co-administration of empty DPPC liposomes and unencapsulated free insulin was investigated in vivo to assess the potential enhancement in protein pulmonary absorption. Co-administration was compared to DPPC liposomes encapsulating insulin, and free insulin.

RESULTS

DPPC liposomes enhanced the pulmonary absorption of unencapsulated free insulin; however, the enhancing effect was lower than that of the DPPC liposomes encapsulating insulin. The mechanism of the pulmonary absorption of unencapsulated free insulin by DPPC liposomes involved the opening of epithelial cell space in alveolar mucosa, and not mucosal cell damage, similar to that of the DPPC liposomes encapsulating insulin. In an in vitro stability test, insulin in the alveolar mucus layer that covers epithelial cells was stable. These findings suggest that, although unencapsulated free insulin spreads throughout the alveolar mucus layer, the concentration of insulin released near the absorption surface is increased by the encapsulation of insulin into DPPC liposomes and the absorption efficiency is also increased.

CONCLUSION

We revealed that the encapsulation of insulin into DPPC liposomes is more effective for pulmonary insulin absorption than co-administration of DPPC liposomes and unencapsulated free insulin.

Development of a Novel Quantitative Structure-Activity Relationship Model to Accurately Predict Pulmonary Absorption and Replace Routine Use of the Isolated Perfused Respiring Rat Lung Model

Purpose

We developed and tested a novel Quantitative Structure-Activity Relationship (QSAR) model to better understand the physicochemical drivers of pulmonary absorption, and to facilitate compound design through improved prediction of absorption. The model was tested using a large array of both existing and newly designed compounds.

Methods

Pulmonary absorption data was generated using the isolated perfused respiring rat lung (IPRLu) model for 82 drug discovery compounds and 17 marketed drugs. This dataset was used to build a novel QSAR model based on calculated physicochemical properties. A further 9 compounds were used to test the model’s predictive capability.

Results

The QSAR model performed well on the 9 compounds in the “Test set” with a predicted versus observed correlation of R² = 0.85, and >65% of compounds correctly categorised. Calculated descriptors associated with permeability and hydrophobicity positively correlated with pulmonary absorption, whereas those associated with charge, ionisation and size negatively correlated.

Conclusions

The novel QSAR model described here can replace routine generation of IPRLu model data for ranking and classifying compounds prior to synthesis. It will also provide scientists working in the field of inhaled drug discovery with a deeper understanding of the physicochemical drivers of pulmonary absorption based on a relevant respiratory compound dataset.

Model-based evaluation of pulmonary pharmacokinetics in asthmatic and COPD patients after oral olodaterol inhalation

AIMS

Olodaterol is an orally inhaled β2 -agonist for treatment of chronic obstructive pulmonary disease (COPD). The aims of this population pharmacokinetic (PK) analysis were: (1) to investigate systemic PK and thereby make inferences about pulmonary PK in asthmatic patients, COPD patients and healthy volunteers, and (2) to assess whether differences in pulmonary efficacy might be expected based on pulmonary PK characteristics.

METHODS

Plasma and urine data after olodaterol inhalation were available from six clinical trials comprising 710 patients and healthy volunteers (single and multiple dosing). To investigate the relevance of covariates, full fixed-effect modelling was applied based on a previously developed healthy volunteer systemic disposition model.

RESULTS

A pulmonary model with three parallel absorption processes best described PK after inhalation in patients. The pulmonary bioavailable fraction (PBIO) was 48.7% (46.1-51.3%, 95% confidence interval) in asthma, and 53.6% (51.1-56.2%) in COPD. In asthma 87.2% (85.4-88.8%) of PBIO was slowly absorbed with an absorption half-life of 18.5 h (16.3-21.4 h), whereas in COPD 80.1% (78.0-82.2%) was absorbed with a half-life of 37.8 h (31.1-47.8 h). In healthy volunteers absorption was faster, with a half-life of 18.5 h (16.3-21.4 h) of the slowest absorbed process, which characterized 74.6% (69.1-80.2%) of PBIO.

CONCLUSIONS

The modelling approach successfully described data after olodaterol inhalation in patients and healthy volunteers. Slow pulmonary absorption was demonstrated both in asthma and COPD. Absorption characteristics after olodaterol inhalation indicated even more beneficial lung targeting in patients compared to healthy volunteers.

Investigating pulmonary and systemic pharmacokinetics of inhaled olodaterol in healthy volunteers using a population pharmacokinetic approach

AIMS

Olodaterol, a novel β2-adrenergic receptor agonist, is a long-acting, once-daily inhaled bronchodilator approved for the treatment of chronic obstructive pulmonary disease. The aim of the present study was to describe the plasma and urine pharmacokinetics of olodaterol after intravenous administration and oral inhalation in healthy volunteers by population pharmacokinetic modelling and thereby to infer its pulmonary fate.

METHODS

Plasma and urine data after intravenous administration (0.5-25 μg) and oral inhalation (2.5-70 μg via the Respimat® inhaler) were available from a total of 148 healthy volunteers (single and multiple dosing). A stepwise model building approach was applied, using population pharmacokinetic modelling. Systemic disposition parameters were fixed to estimates obtained from intravenous data when modelling data after inhalation.

RESULTS

A pharmacokinetic model, including three depot compartments with associated parallel first-order absorption processes (pulmonary model) on top of a four-compartment body model (systemic disposition model), was found to describe the data the best. The dose reaching the lung (pulmonary bioavailable fraction) was estimated to be 49.4% [95% confidence interval (CI) 46.1, 52.7%] of the dose released from the device. A large proportion of the pulmonary bioavailable fraction [70.1% (95% CI 66.8, 73.3%)] was absorbed with a half-life of 21.8 h (95% CI 19.7, 24.4 h).

CONCLUSIONS

The plasma and urine pharmacokinetics of olodaterol after intravenous administration and oral inhalation in healthy volunteers were adequately described. The key finding was that a high proportion of the pulmonary bioavailable fraction had an extended pulmonary residence time. This finding was not expected based on the physicochemical properties of olodaterol.

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.

Pharmacometric Models for Characterizing the Pharmacokinetics of Orally Inhaled Drugs

During the last decades, the importance of modeling and simulation in clinical drug development, with the goal to qualitatively and quantitatively assess and understand mechanisms of pharmacokinetic processes, has strongly increased. However, this increase could not equally be observed for orally inhaled drugs. The objectives of this review are to understand the reasons for this gap and to demonstrate the opportunities that mathematical modeling of pharmacokinetics of orally inhaled drugs offers. To achieve these objectives, this review (i) discusses pulmonary physiological processes and their impact on the pharmacokinetics after drug inhalation, (ii) provides a comprehensive overview of published pharmacokinetic models, (iii) categorizes these models into physiologically based pharmacokinetic (PBPK) and (clinical data-derived) empirical models, (iv) explores both their (mechanistic) plausibility, and (v) addresses critical aspects of different pharmacometric approaches pertinent for drug inhalation. In summary, pulmonary deposition, dissolution, and absorption are highly complex processes and may represent the major challenge for modeling and simulation of PK after oral drug inhalation. Challenges in relating systemic pharmacokinetics with pulmonary efficacy may be another factor contributing to the limited number of existing pharmacokinetic models for orally inhaled drugs. Investigations comprising in vitro experiments, clinical studies, and more sophisticated mathematical approaches are considered to be necessary for elucidating these highly complex pulmonary processes. With this additional knowledge, the PBPK approach might gain additional attractiveness. Currently, (semi-)mechanistic modeling offers an alternative to generate and investigate hypotheses and to more mechanistically understand the pulmonary and systemic pharmacokinetics after oral drug inhalation including the impact of pulmonary diseases.

The lung as a route for systemic delivery of therapeutic proteins and peptides

The large surface area, good vascularization, immense capacity for solute exchange and ultra-thinness of the alveolar epithelium are unique features of the lung that can facilitate systemic delivery via pulmonary administration of peptides and proteins. Physical and biochemical barriers, lack of optimal dosage forms and delivery devices limit the systemic delivery of biotherapeutic agents by inhalation. Current efforts to overcome these difficulties in order to deliver metabolic hormones (insulin, calcitonin, thyroid-stimulating hormone [TSH], follicle-stimulating hormone [FSH] and growth hormones) systemically, to induce systemic responses (immunoglobulins, cyclosporin A [CsA], recombinant-methionyl human granulocyte colony-stimulating factor [r-huG-CSF], pancreatic islet autoantigen) and to modulate other biological processes via the lung are reviewed. Safety aspects of pulmonary peptide and protein administration are also discussed.