Deposition of coarse particles in cystic fibrosis: model predictions versus experimental results

Derivation of first-order dissolution rates to estimate particle clearance and burden in the human respiratory tract

Inhalation is a portal-of-entry for aerosols via the respiratory tract where particulate burden accumulates depending on sites of particle deposition, normal clearance mechanisms, and particle solubility. The time available for dissolution of particles is determined by the balance between the rate of particle clearance from a region and their solubility in respiratory solvents. Dissolution is a function of particle surface area divided by particle volume or mass (i.e., dissolution is inversely proportional to the physical diameter of particles). As a conservative approach, investigators commonly assume the complete and instantaneous dissolution of metals from particles depositing in the alveolar region of the respiratory tract. We derived first-order dissolution rate constants to facilitate biokinetic modeling of particle clearance, dissolution, and absorption into the blood. We then modeled pulmonary burden and total dissolution of particles over time as a function of particle size, density, and solubility. We show that assuming poorly soluble particle forms will enter the blood as quickly as highly soluble forms causes an overestimation of concentrations of the compound of interest in blood and other extrapulmonary tissues while also underestimating its pulmonary burden. We conclude that, in addition to modeling dose rates for particle deposition into the lung, physiologically based pharmacokinetic modeling of pulmonary and extrapulmonary tissues concentrations of moderately and poorly soluble materials can be improved by including estimates of lung burden and particle dissolution over time.

Shaping the future from the small scale: dry powder inhalation of CRISPR-Cas9 lipid nanoparticles for the treatment of lung diseases

INTRODUCTION

Most lung diseases are serious conditions resulting from genetic and environmental causes associated with high mortality and severe symptoms. Currently, treatments available have a palliative effect and many targets are still considered undruggable. Gene therapy stands as an attractive approach to offering innovative therapeutic solutions. CRISPRCas9 has established a remarkable potential for genome editing with high selectivity to targeted mutations. To ensure high efficacy with minimum systemic exposure, the delivery and administration route are key components that must be investigated.

AREAS COVERED

This review is focused on the delivery of CRISPRCas9 to the lungs, taking advantage of lipid nanoparticles (LNPs), the most clinically advanced nucleic acid carriers. We also aim to highlight the benefits of pulmonary administration as a local delivery route and the use of spray drying to prepare stable nucleic-acid-based dry powder formulations that can overcome multiple lung barriers.

EXPERT OPINION

Exploring the pulmonary administration to deliver CRISPRCas9 loaded in LNPs as a dry powder increases the chances to achieve high efficacy and reduced adverse effects. CRISPRCas9 loaded in LNP-embedded microparticles has not yet been reported in the literature but has the potential to reach and accumulate in target cells in the lung, thus, enhancing overall efficacy and safety.

Aerosolizing Lipid Dispersions Enables Antibiotic Transport Across Mimics of the Lung Airway Surface Even in the Presence of Pre-existing Lipid Monolayers

BACKGROUND

Secondary lung infections are the primary cause of morbidity associated with cystic fibrosis lung disease. Aerosolized antibiotic inhalation is potentially advantageous but has limited effectiveness due to altered airway aerodynamics and deposition patterns that limit drug access to infected regions. One potential strategy to better reach infected areas is to formulate aerosols with surfactants that induce surface tension gradients and drive postdeposition drug dispersal via Marangoni transport along the airway surface liquid (ASL). Since this relies on surfactant-induced surface tension reduction, the presence of endogenous lipid monolayers may hinder drug dispersal performance.

METHODS

Tobramycin solutions were formulated with dipalmitoylphosphatidylcholine (DPPC), a major component of endogenous pulmonary surfactant, to drive postdeposition aerosol dispersal across a model ASL based on a liquid layer or "subphase" of aqueous porcine gastric mucin (PGM) solution with predeposited DPPC monolayers to mimic the endogenous surfactant. In vitro subphase samples were collected from regions outside the aerosol deposition zone and assayed for tobramycin concentration using a closed enzyme donor immunoassay. The motion of a tracking bead across the subphase surface and the corresponding decrease in surface tension on aerosol deposition were tracked both with and without a predeposited DPPC monolayer. The surface tension/area isotherm for DPPC on PGM solution subphase was measured to aid in the interpretation of the tobramycin dispersal behavior.

RESULTS AND CONCLUSIONS

Transport of tobramycin away from the deposition region occurs in aerosols formulated with DPPC whether or not predeposited lipid is present, and tobramycin concentrations are similar in both cases across biologically relevant length scales (∼8 cm). When DPPC is deposited from an aerosol, it induces ultralow surface tensions (<5 mN/m), which drive Marangoni flows, even in the presence of a dense background layer of DPPC. Therefore, aerosolized phospholipids, such as DPPC, will likely be effective spreading agents in the human lung.

Heterogeneity of Particle Deposition by Pixel Analysis of 2D Gamma Scintigraphy Images

BACKGROUND

Heterogeneity of inhaled particle deposition in airways disease may be a sensitive indicator of physiologic changes in the lungs. Using planar gamma scintigraphy, we developed new methods to locate and quantify regions of high (hot) and low (cold) particle deposition in the lungs.

METHODS

Initial deposition and 24 hour retention images were obtained from healthy (n=31) adult subjects and patients with mild cystic fibrosis lung disease (CF) (n=14) following inhalation of radiolabeled particles (Tc99m-sulfur colloid, 5.4 μm MMAD) under controlled breathing conditions. The initial deposition image of the right lung was normalized to (i.e., same median pixel value), and then divided by, a transmission (Tc99m) image in the same individual to obtain a pixel-by-pixel ratio image. Hot spots were defined where pixel values in the deposition image were greater than 2X those of the transmission, and cold spots as pixels where the deposition image was less than 0.5X of the transmission. The number ratio (NR) of the hot and cold pixels to total lung pixels, and the sum ratio (SR) of total counts in hot pixels to total lung counts were compared between healthy and CF subjects. Other traditional measures of regional particle deposition, nC/P and skew of the pixel count histogram distribution, were also compared.

RESULTS

The NR of cold spots was greater in mild CF, 0.221±0.047(CF) vs. 0.186±0.038 (healthy) (p<0.005) and was significantly correlated with FEV1 %pred in the patients (R=-0.70). nC/P (central to peripheral count ratio), skew of the count histogram, and hot NR or SR were not different between the healthy and mild CF patients.

CONCLUSIONS

These methods may provide more sensitive measures of airway function and localization of deposition that might be useful for assessing treatment efficacy in these patients.

Theoretical models for the simulation of particle deposition and tracheobronchial clearance in lungs of patients with chronic bronchitis

INTRODUCTION

Based upon theoretical models particle deposition and clearance in human respiratory systems affected by chronic bronchitis can be approximated reliably. As a consequence of those hypothetical results, optimal frame conditions (e.g., inhalation time and volume, particle properties) for inhalation therapies can be determined.

METHODS

Simulation of particle deposition was conducted by modelling a partly or fully obstructed tracheobronchial architecture. Bronchitis-induced reductions of the airway calibres were computed by application of specific scaling factors. Three different scenarios of chronic bronchitis were modelled. Brownian motion, inertial impaction, interception, and gravitational settling were assumed as main deposition forces influencing inhaled particular mass. Tracheobronchial clearance was approximated by application of generation-specific mucus velocities as well as the consideration of a slow bronchial clearance phase, whose half-time varied between 5 and 20 days.

RESULTS

Under different breathing conditions (i.e., sitting and light-work breathing) deposition of submicron and µm-sized particles is significantly enhanced within the bronchial lung region, but also alveolar deposition becomes partly enhanced. By changing the inhalation conditions target sites of therapeutic aerosols may be reached with rather high accuracy. Based on the data of this modified models, particle retention in lung airways of patients suffering from chronic bronchitis may be noticeably prolonged, with 24-hour retention values being increased by up to 50%.

DISCUSSION AND CONCLUSIONS

As exhibited by the results, particle deposition behaviour in lungs affected by chronic bronchitis differs remarkably from that in healthy lungs. These theoretical finds are mostly supported by experimental data. Further, experimental and theoretical deposition results may be used for an estimation of the grade of disease. Tracheobronchial clearance reduces its efficiency with each progress of the disease which increases the probability of bacterial infections in the airways.

Biokinetics of nanoparticles and susceptibility to particulate exposure in a murine model of cystic fibrosis

BACKGROUND

Persons with cystic fibrosis (CF) are at-risk for health effects from ambient air pollution but little is known about the interaction of nanoparticles (NP) with CF lungs. Here we study the distribution of inhaled NP in a murine CF model and aim to reveal mechanisms contributing to adverse effects of inhaled particles in susceptible populations.

METHODS

Chloride channel defective CftrTgH (neoim) Hgu mice were used to analyze lung function, lung distribution and whole body biokinetics of inhaled NP, and inflammatory responses after intratracheal administration of NP. Distribution of 20-nm titanium dioxide NP in lungs was assessed on ultrathin sections immediately and 24 h after a one-hour NP inhalation. NP biokinetics was deduced from total and regional lung deposition and from whole body translocation of inhaled 30-nm iridium NP within 24 h after aerosol inhalation. Inflammatory responses were assessed within 7 days after carbon NP instillation.

RESULTS

Cftr mutant females had moderately reduced lung compliance and slightly increased airway resistance compared to wild type mice. We found no genotype dependent differences in total, regional and head deposition or in secondary-organ translocation of inhaled iridium NP. Titanium dioxide inhalation resulted in higher NP uptake by alveolar epithelial cells in Cftr mutants. Instillation of carbon NP induced a comparable acute and transient inflammatory response in both genotypes. The twofold increase of bronchoalveolar lavage (BAL) neutrophils in Cftr mutant compared to wild type mice at day 3 but not at days 1 and 7, indicated an impaired capacity in inflammation resolution in Cftr mutants. Concomitant to the delayed decline of neutrophils, BAL granulocyte-colony stimulating factor was augmented in Cftr mutant mice. Anti-inflammatory 15-hydroxyeicosatetraenoic acid was generally significantly lower in BAL of Cftr mutant than in wild type mice.

CONCLUSIONS

Despite lacking alterations in lung deposition and biokinetics of inhaled NP, and absence of significant differences in lung function, higher uptake of NP by alveolar epithelial cells and prolonged, acute inflammatory responses to NP exposure indicate a moderately increased susceptibility of lungs to adverse effects of inhaled NP in Cftr mutant mice and provides potential mechanisms for the increased susceptibility of CF patients to air pollution.

Early airway structural changes in cystic fibrosis pigs as a determinant of particle distribution and deposition

The pathogenesis of cystic fibrosis (CF) airway disease is not well understood. A porcine CF model was recently generated, and these animals develop lung disease similar to humans with CF. At birth, before infection and inflammation, CF pigs have airways that are irregularly shaped and have a reduced caliber compared to non-CF pigs. We hypothesized that these airway structural abnormalities affect airflow patterns and particle distribution. To test this hypothesis we used computational fluid dynamics (CFD) on airway geometries obtained by computed tomography of newborn non-CF and CF pigs. For the same flow rate, newborn CF pig airways exhibited higher air velocity and resistance compared to non-CF. Moreover we found that, at the carina bifurcation, particles greater than 5-μm preferably distributed to the right CF lung despite almost equal airflow ventilation in non-CF and CF. CFD modeling also predicted that deposition efficiency was greater in CF compared to non-CF for 5- and 10-μm particles. These differences were most significant in the airways included in the geometry supplying the right caudal, right accessory, left caudal, and left cranial lobes. The irregular particle distribution and increased deposition in newborn CF pig airways suggest that early airway structural abnormalities might contribute to CF disease pathogenesis.

Pulmonary drug delivery: medicines for inhalation

Mankind has inhaled substances for medical and other reasons for thousands of years, notably resulting in the cultural manifestations of tobacco and opium smoking. Over the course of time concepts of pulmonary application, including inhalation devices and drug formulations, have been and still are being continuously developed. State of the art instruments even allow for individualized drug application by adaptation of the inhalation procedure to the breathing pattern of the patient. Pulmonary drug delivery offers promising advantages in comparison to "classical" drug administration via the oral or transcutaneous routes, which is also reflected by an increasing interest and number of marketed products for inhalation therapy. However, the lungs' efficient clearance mechanisms still limit the benefit of many therapeutic concepts. In consequence the objective of current research and development in pulmonary drug delivery is to overcome and to control drug clearance from the intended target site. Here, several of the most auspicious future drug delivery concepts are presented and discussed in order to give the reader an insight into this emerging field of medicine.

Toward modern inhalational bacteriophage therapy: nebulization of bacteriophages of Burkholderia cepacia complex

Antibiotic-resistant bacterial infections have renewed interest in finding substitute methods of treatment. The purpose of the present in vitro study was to investigate the possibility of respiratory delivery of a Burkholderia cepacia complex (BCC) bacteriophage by nebulized aerosol administration. Bacteriophages in isotonic saline were aerosolized with Pari LC star and eFlow nebulizers, at titers with mean value (standard deviation) of 2.15 x 10(8) (1.63 x 10(8)) plaque-forming unit (PFU)/mL in 2.5-mL nebulizer fills. The breathing pattern of an adult was simulated using a pulmonary waveform generator. During breath simulation, the size distributions of the nebulized aerosol were measured using phase doppler anemometry (PDA). Efficiency of nebulizer delivery was subsequently determined by collection of aerosol on low resistance filters and measurement of bacteriophage titers. These filter titers were used as input data to a mathematical lung deposition model to predict regional deposition of bacteriophages in the lung and initial bacteriophage titers in the liquid surface layer of each conducting airway generation. The results suggest that BCC bacteriophages can be nebulized successfully within a reasonable delivery time and predicted titers in the lung indicate that this method may hold potential for treatment of bacterial lung infections common among cystic fibrosis patients.

Recent advances in predictive understanding of respiratory tract deposition

Accurate prediction of respiratory tract deposition is important in gauging the health risks of ambient bioaerosols and environmental aerosols, as well as in developing pharmaceutical aerosols for drug delivery. The present article highlights recent advances in the prediction of total, extrathoracic, and lung deposition fractions of inhaled aerosols over a broad range of parameters for both oral and nasal breathing. These advances build on recent data from in vivo and in vitro studies that have benefited from recent improvements in high-resolution imaging, rapid prototyping, and computational simulation abilities that have significantly enhanced the current understanding of respiratory tract deposition. It is anticipated that the relatively simple equations for predicting total or whole lung deposition that follow from the recent work discussed herein will allow for improved correlation between respiratory tract deposition and a wide range of health outcomes.

Modeling airflow and particle transport/deposition in pulmonary airways

A review of research papers is presented, pertinent to computer modeling of airflow as well as nano- and micron-size particle deposition in pulmonary airway replicas. The key modeling steps are outlined, including construction of suitable airway geometries, mathematical description of the air-particle transport phenomena and computer simulation of micron and nanoparticle depositions. Specifically, diffusion-dominated nanomaterial deposits on airway surfaces much more uniformly than micron particles of the same material. This may imply different toxicity effects. Due to impaction and secondary flows, micron particles tend to accumulate around the carinal ridges and to form "hot spots", i.e., locally high concentrations which may lead to tumor developments. Inhaled particles in the size range of 20nm< or =dp< or =3microm may readily reach the deeper lung region. Concerning inhaled therapeutic particles, optimal parameters for mechanical drug-aerosol targeting of predetermined lung areas can be computed, given representative pulmonary airways.

Controlled inhalation of aerosolised therapeutics

With the advent of new, and often expensive, therapeutics designed for aerosol delivery to the lung, there is a need to improve the targeting and efficiency of their delivery. By controlling breathing patterns associated with inhaled aerosols, it has been shown that deposition in the lung can be both maximised and targeted to specific lung regions. A new commercially available device, the AKITA (Inamed GmbH) allows for individualised, controlled inhalation of aerosols produced by conventional nebulisers. Smart card technology is incorporated into the AKITA to both individualise breathing patterns as well as record compliance of therapy. So far, the use of this new device has provided maximal delivery of drug to the lung, with improved patient compliance and minimal waste of drug.