Rapid transport of large polymeric nanoparticles in fresh undiluted human mucus

Carrier interactions with the biological barriers of the lung: advanced in vitro models and challenges for pulmonary drug delivery

In recent years significant progress has been made to improve particle deposition in the lung. However, the development of strategies to overcome the air-blood lung barrier is still needed. The combination of complex in vitro models and sophisticated particulate carriers is promising as a strategy by which that goal could be achieved. In this review we discuss currently available in vitro lung models, including some recent tissue-engineering approaches, as well as the challenges associated to implement such complex in vitro systems. Furthermore, we discuss available carrier technologies, often based on nanotechnology, to target specific regions of the lungs and to overcome the respective biological barriers, ideally resulting in safe and effective delivery to the desired pulmonary destination.

Nanoparticle penetration of human cervicovaginal mucus: the effect of polyvinyl alcohol

Therapeutic nanoparticles must rapidly penetrate the mucus secretions lining the surfaces of the respiratory, gastrointestinal and cervicovaginal tracts to efficiently reach the underlying tissues. Whereas most polymeric nanoparticles are highly mucoadhesive, we previously discovered that a dense layer of low MW polyethylene glycol (PEG) conferred a sufficiently hydrophilic and uncharged surface to effectively minimize mucin-nanoparticle adhesive interactions, allowing well-coated particles to rapidly diffuse through human mucus. Here, we sought to investigate the influence of surface coating by polyvinyl alcohol (PVA), a relatively hydrophilic and uncharged polymer routinely used as a surfactant to formulate drug carriers, on the transport of nanoparticles in fresh human cervicovaginal mucus. We found that PVA-coated polystyrene (PS) particles were immobilized, with speeds at least 4000-fold lower in mucus than in water, regardless of the PVA molecular weight or incubation concentration tested. Nanoparticles composed of poly(lactide-co-glycolide) (PLGA) or diblock copolymers of PEG-PLGA were similarly immobilized when coated with PVA (slowed 29,000- and 2500-fold, respectively). PVA coatings could not be adequately removed upon washing, and the residual PVA prevented sufficient coating with Pluronic F127 capable of reducing particle mucoadhesion. In contrast to PVA-coated particles, the similar sized PEG-coated formulations were slowed only ~6- to 10-fold in mucus compared to in water. Our results suggest that incorporating PVA in the particle formulation process may lead to the formation of mucoadhesive particles for many nanoparticulate systems. Thus, alternative methods for particle formulation, based on novel surfactants or changes in the formulation process, should be identified and developed in order to produce mucus-penetrating particles for mucosal applications.

Vaginal delivery of paclitaxel via nanoparticles with non-mucoadhesive surfaces suppresses cervical tumor growth

Local delivery of chemotherapeutics in the cervicovaginal tract using nanoparticles may reduce adverse side effects associated with systemic chemotherapy, while improving outcomes for early-stage cervical cancer. It is hypothesized here that drug-loaded nanoparticles that rapidly penetrate cervicovaginal mucus (CVM) lining the female reproductive tract will more effectively deliver their payload to underlying diseased tissues in a uniform and sustained manner compared with nanoparticles that do not efficiently penetrate CVM. Paclitaxel-loaded nanoparticles are developed, composed entirely of polymers used in FDA-approved products, which rapidly penetrate human CVM and provide sustained drug release with minimal burst effect. A mouse model is further employed with aggressive cervical tumors established in the cervicovaginal tract to compare paclitaxel-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (conventional particles, or CP) and similar particles coated with Pluronic F127 (mucus-penetrating particles, or MPP). CP are mucoadhesive and, thus, aggregated in mucus, while MPP achieve more uniform distribution and close proximity to cervical tumors. Paclitaxel-MPP suppress tumor growth more effectively and prolong median survival of mice compared with unencapsulated paclitaxel or paclitaxel-CP. Histopathological studies demonstrate minimal toxicity to the cervicovaginal epithelia, suggesting paclitaxel-MPP may be safe for intravaginal use. These results demonstrate the in vivo advantages of polymer-based MPP for treatment of tumors localized to a mucosal surface.

Non-invasive delivery of stealth, brain-penetrating nanoparticles across the blood-brain barrier using MRI-guided focused ultrasound

The blood-brain barrier (BBB) presents a significant obstacle for the treatment of many central nervous system (CNS) disorders, including invasive brain tumors, Alzheimer's, Parkinson's and stroke. Therapeutics must be capable of bypassing the BBB and also penetrate the brain parenchyma to achieve a desired effect within the brain. In this study, we test the unique combination of a non-invasive approach to BBB permeabilization with a therapeutically relevant polymeric nanoparticle platform capable of rapidly penetrating within the brain microenvironment. MR-guided focused ultrasound (FUS) with intravascular microbubbles (MBs) is able to locally and reversibly disrupt the BBB with submillimeter spatial accuracy. Densely poly(ethylene-co-glycol) (PEG) coated, brain-penetrating nanoparticles (BPNs) are long-circulating and diffuse 10-fold slower in normal rat brain tissue compared to diffusion in water. Following intravenous administration of model and biodegradable BPNs in normal healthy rats, we demonstrate safe, pressure-dependent delivery of 60nm BPNs to the brain parenchyma in regions where the BBB is disrupted by FUS and MBs. Delivery of BPNs with MR-guided FUS has the potential to improve efficacy of treatments for many CNS diseases, while reducing systemic side effects by providing sustained, well-dispersed drug delivery into select regions of the brain.

Single particle tracking reveals biphasic transport during nanorod magnetophoresis through extracellular matrix

Magnetic drug targeting has been proposed as a means of efficiently targeting drugs to tumors. However, the extracellular matrix (ECM) remains a significant barrier to long-range magnetophoretic transport through the tumor volume. While ensemble measurements of nanoparticle magnetophoresis have been reported, a single particle level understanding of magnetophoretic transport remains at large. We quantify nanorod magnetophoresis through ECM based on single particle observations. We find that smaller diameter particles achieve larger velocities through ECM despite experiencing smaller magnetic forces. Additionally, two interesting dynamics are elucidated. First, 18 nm diameter nanorods experience bimodal stick-slip motion through ECM during static field magnetophoresis, while similar bimodal transport is not observed for 55 nm nor 200 nm diameter nanorods. Second, smaller particles experience larger deviations in their orientation angle with respect to the magnetic field. This work elucidates important dynamics of nanoparticle transport through complex, porous biomaterials that may go unnoticed during ensemble measurements.

Altered goblet cell differentiation and surface mucus properties in Hirschsprung disease

Hirschsprung disease-associated enterocolitis (HAEC) leads to significant mortality and morbidity, but its pathogenesis remains unknown. Changes in the colonic epithelium related to goblet cells and the luminal mucus layer have been postulated to play a key role. Here we show that the colonic epithelium of both aganglionic and ganglionic segments are altered in patients and in mice with Hirschsprung disease (HSCR). Structurally, goblet cells were altered with increased goblet cell number and reduced intracellular mucins in the distal colon of biopsies from patients with HSCR. Endothelin receptor B (Ednrb) mutant mice showed increased goblet cell number and size and increased cell proliferation compared to wild-type mice in aganglionic segments, and reduced goblet cell size and number in ganglionic segments. Functionally, compared to littermates, Ednrb^−/− mice showed increased transepithelial resistance, reduced stool water content and similar chloride secretion in the distal colon. Transcript levels of goblet cell differentiation factors SPDEF and Math1 were increased in the distal colon of Ednrb^−/− mice. Both distal colon from Ednrb mice and biopsies from HSCR patients showed reduced Muc4 expression as compared to controls, but similar expression of Muc2. Particle tracking studies showed that mucus from Ednrb^−/− mice provided a more significant barrier to diffusion of 200 nm nanoparticles as compared to wild-type mice. These results suggest that aganglionosis is associated with increased goblet cell proliferation and differentiation and subsequent altered surface mucus properties, prior to the development of inflammation in the distal colon epithelium. Restoration of normal goblet cell function and mucus layer properties in the colonic epithelium may represent a therapeutic strategy for prevention of HAEC.

Adenoviral vectors coated with cationic PEG derivatives for intravaginal vaccination against HIV-1

Mucus layer coating the vaginal epithelium represents a barrier for intravaginally delivered recombined adenoviral (rAd) vectors, but it could be overcome by proper polyethylene glycol (PEG) modification. Here we synthesized two cationic PEG derivatives, amino-(EO)n/(AGE)m-Cyss (APCs). The polymers contained neutral linear PEG (2-5 kDa) to provide a hydrophilic surface and amine pendants to provide positive charge for coating negatively charged rAd by physical adsorption. Given proper molecular composition, the polymer (5k-APC) could coat rAd without causing aggregation, facilitating its mucus penetrating ability and enhancing gene expression both in vitro and in vivo. With HIVgag as the model antigen, the polymer-rAd complexes were administered intravaginally to elicit both systemic and mucosal immune responses. 5k-APC-rAd immunization elicited robust HIVgag-specific cellular responses and also induced higher antigen-specific serum IgG. More importantly, mice immunized with 5k-APC-rAd showed higher level of IgA in vaginal lavage fluid. These findings suggest that 5k-APC-rAd is a promising system for intravaginal immunization against infectious diseases such as HIV within the vaginal tract.

Modified-chitosan/siRNA nanoparticles downregulate cellular CDX2 expression and cross the gastric mucus barrier

Development of effective non-viral vectors is of crucial importance in the implementation of RNA interference in clinical routine. The localized delivery of siRNAs to the gastrointestinal mucosa is highly desired but faces specific problems such as the stability in gastric acidity conditions and the presence of the mucus barrier. CDX2 is a transcription factor critical for intestinal differentiation being involved in the initiation and maintenance of gastrointestinal diseases. Specifically, it is the trigger of gastric intestinal metaplasia which is a precursor lesion of gastric cancer. Its expression is also altered in colorectal cancer, where it may constitute a lineage-survival oncogene. Our main objective was to develop a nanoparticle-delivery system of siRNA targeting CDX2 using modified chitosan as a vector. CDX2 expression was assessed in gastric carcinoma cell lines and nanoparticles behaviour in gastrointestinal mucus was tested in mouse explants. We show that imidazole-modified chitosan and trimethylchitosan/siRNA nanoparticles are able to downregulate CDX2 expression and overpass the gastric mucus layer but not colonic mucus. This system might constitute a potential therapeutic approach to treat CDX2-dependent gastric lesions.

Alterations in mucus barrier function and matrix structure induced by guluronate oligomers

The effect of guluronate oligomers on the barrier properties of mucous matrices was investigated in terms of the mobility of nanoparticles in mucous matrices by fluorescence recovery after photobleaching (FRAP), cellular uptake of nanoparticles in mucus secreting cells (HT29-MTX), and mucin matrix architecture by scanning electron microscopy (SEM). Guluronate oligomers improved nanoparticle mobility in both native and highly purified mucus matrices and improved cellular uptake of nanoparticles through a mucus layer. Addition of guluronate oligomers to mucin matrices resulted in a decrease in the density of network cross-links and an increase in matrix pore size. Based on these data, we conclude that guluronate oligomers are able to improve nanoparticle mobility in several mucus matrices and alter network architecture in mucin matrices in a manner that suggests a reduction in barrier function. As such, there may be a potential application for guluronate oligomers in mucosal delivery of nanomedicines.

Nano/micro and spectroscopic approaches to food pathogen detection

Despite continuing research efforts, timely and simple pathogen detection with a high degree of sensitivity and specificity remains an elusive goal. Given the recent explosion of sensor technologies, significant strides have been made in addressing the various nuances of this important global challenge that affects not only the food industry but also human health. In this review, we provide a summary of the various ongoing efforts in pathogen detection and sample preparation in areas related to Fourier transform infrared and Raman spectroscopy, light scattering, phage display, micro/nanodevices, and nanoparticle biosensors. We also discuss the advantages and potential limitations of the detection methods and suggest next steps for further consideration.

Nicotine alters mucin rheological properties

Tobacco smoke exposure, the major cause of chronic obstructive pulmonary disease (COPD), instigates a dysfunctional clearance of thick obstructive mucus. However, the mechanism underlying the formation of abnormally viscous mucus remains elusive. We investigated whether nicotine can directly alter the rheological properties of mucin by examining its physicochemical interactions with human airway mucin gels secreted from A549 lung epithelial cells. Swelling kinetics and multiple particle tracking were utilized to assess mucin gel viscosity change when exposed to nicotine. Herein we show that nicotine (≤50 nM) significantly hindered postexocytotic swelling and hydration of released mucins, leading to higher viscosity, possibly by electrostatic and hydrophobic interactions. Moreover, the close association of nicotine and mucins allows airway mucus to function as a reservoir for prolonged nicotine release, leading to correlated pathogenic effects. Our results provide a novel explanation for the maltransport of poorly hydrated mucus in smokers. More importantly, this study further indicates that even low-concentration nicotine can profoundly increase mucus viscosity and thus highlights the health risks of secondhand smoke exposure.

Nanoparticle-based drug delivery to the vagina: a review

Vaginal drug administration can improve prophylaxis and treatment of many conditions affecting the female reproductive tract, including sexually transmitted diseases, fungal and bacterial infections, and cancer. However, achieving sustained local drug concentrations in the vagina can be challenging, due to the high permeability of the vaginal epithelium and expulsion of conventional soluble drug dosage forms. Nanoparticle-based drug delivery platforms have received considerable attention for vaginal drug delivery, as nanoparticles can provide sustained release, cellular targeting, and even intrinsic antimicrobial or adjuvant properties that can improve the potency and/or efficacy of prophylactic and therapeutic modalities. Here, we review the use of polymeric nanoparticles, liposomes, dendrimers, and inorganic nanoparticles for vaginal drug delivery. Although most of the work toward nanoparticle-based drug delivery in the vagina has been focused on HIV prevention, strategies for treatment and prevention of other sexually transmitted infections, treatment for reproductive tract cancer, and treatment of fungal and bacterial infections are also highlighted.

Drug delivery strategies in the therapy of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a frequently occurring disease in young people, which is characterized by a chronic inflammation of the gastrointestinal tract. The therapy of IBD is dominated by the administration of anti-inflammatory and immunosuppressive drugs, which suppress the intestinal inflammatory burden and improve the disease-related symptoms. Established treatment strategies are characterized by a limited therapeutical efficacy and the occurrence of adverse drug reactions. Thus, the development of novel disease-targeted drug delivery strategies is intended for a more effective therapy and demonstrates the potential to address unmet medical needs. This review gives an overview about the established as well as future-oriented drug targeting strategies, including intestine targeting by conventional drug delivery systems (DDS), disease targeted drug delivery by synthetic DDS and disease targeted drug delivery by biological DDS. Furthermore, this review analyses the targeting mechanisms of the respective DDS and discusses the possible field of utilization in IBD.

Dextran-protamine coated nanostructured lipid carriers as mucus-penetrating nanoparticles for lipophilic drugs

The main objectives of the present study were (i) to evaluate the effect of the mucus layer on saquinavir-loaded nanostructured lipid carriers (SQV-NLCs) uptake and (ii) to evaluate the mucopenetrating properties of dextran-protamine (Dex-Prot) coating on NLCs as per SQV permeability enhancement. Three different NLC formulations differing on particle size and surfactant content were obtained and coated with Dex-Prot complexes. SQV permeability was then evaluated across Caco-2 cell monolayers (enterocyte-like model) and Caco-2/HT29-MTX cell monolayers (mucus model). In the Caco-2 monolayers, Dex-Prot-NLCs increased up to 9-fold SQV permeability in comparison to uncoated nanoparticles. In the Caco-2/HT29-MTX monolayers, Dex-Prot-NLCs presenting a surface charge close to neutrality significantly increased SQV permeability. Hence, Dex-Prot complex coating is a promising strategy to ensure successful nanoparticle mucus-penetration, and thus, an efficient nanoparticle oral delivery. To our knowledge, this is the first time that Dex-Prot coating has been described as a nanoparticle muco-penetration enhancer across the intestinal mucus barrier.

Spatial configuration and composition of charge modulates transport into a mucin hydrogel barrier

The mucus barrier is selectively permeable to a wide variety of molecules, proteins, and cells, and establishes gradients of these particulates to influence the uptake of nutrients, the defense against pathogens, and the delivery of drugs. Despite its importance for health and disease, the criteria that govern transport through the mucus barrier are largely unknown. Studies with uniformly functionalized nanoparticles have provided critical information about the relevance of particle size and net charge for mucus transport. However, these particles lack the detailed spatial arrangements of charge found in natural mucus-interacting substrates, such as certain viruses, which may have important consequences for transport through the mucus barrier. Using a novel, to our knowledge, microfluidic design that enables us to measure real-time transport gradients inside a hydrogel of mucins, the gel-forming glycoprotein component of mucus, we show that two peptides with the same net charge, but different charge arrangements, exhibit fundamentally different transport behaviors. Specifically, we show that certain configurations of positive and negative charges result in enhanced uptake into a mucin barrier, a remarkable effect that is not observed with either charge alone. Moreover, we show that the ionic strength within the mucin barrier strongly influences transport specificity, and that this effect depends on the detailed spatial arrangement of charge. These findings suggest that spatial charge distribution is a critical parameter to modulate transport through mucin-based barriers, and have concrete implications for the prediction of mucosal passage, and the design of drug delivery vehicles with tunable transport properties.

Challenges associated with Penetration of Nanoparticles across Cell and Tissue Barriers: A Review of Current Status and Future Prospects

Nanoparticles (NPs) have emerged as an effective modality for the treatment of various diseases including cancer, cardiovascular and inflammatory diseases. Various forms of NPs including liposomes, polymer particles, micelles, dendrimers, quantum dots, gold NPs and carbon nanotubes have been synthesized and tested for therapeutic applications. One of the greatest challenges that limit the success of NPs is their ability to reach the therapeutic site at necessary doses while minimizing accumulation at undesired sites. The biodistribution of NPs is determined by body's biological barriers that manifest in several distinct ways. For intravascular delivery of NPs, the barrier manifests in the form of: (i) immune clearance in the liver and spleen, (ii) permeation across the endothelium into target tissues, (iii) penetration through the tissue interstitium, (iv) endocytosis in target cells, (v) diffusion through cytoplasm and (vi) eventually entry into the nucleus, if required. Certain applications of NPs also rely on delivery through alternate routes including skin and mucosal membranes of the nose, lungs, intestine and vagina. In these cases, the diffusive resistance of these tissues poses a significant barrier to delivery. This review focuses on the current understanding of penetration of NPs through biological barriers. Emphasis is placed on transport barriers and not immunological barriers. The review also discusses design strategies for overcoming the barrier properties.

Development and in vitro evaluation of slippery nanoparticles for enhanced diffusion through native mucus

Aim: The aim of this study was to investigate the mucus-penetrating properties of neutral nanoparticles comprising poly(acrylic acid) (PAA) and poly(allylamine) (PAM). Materials & methods: PAA and PAM nanoparticles were prepared on the basis of ionic interactions between the two polymers. Nanoparticles were characterized by particle size as well as surface charge. The cytotoxicity was examined via resazurin and lactate dehydrogenase assays. Using a modified Ussing chamber with mucus, the diffusion properties of obtained neutral nanoparticles were compared with control particles. Results: The obtained PAA–PAM nanoparticles demonstrated no significant cytotoxicity and displayed smooth and spherical surfaces, a particle size range of 200 nm and ζ-potential of 0.9 mV. The diffusion efficiency of neutral nanoparticles was 2.5- and 1.8-fold higher than PAM and PAA nanoparticles, respectively. Conclusion: Taking enhanced mucus-penetrating properties into account, neutral nanoparticles were shown to be very promising in drug delivery via mucus membranes of different cavities.

Original submitted 30 May 2012; Revised submitted 21 November 2012; Published online 23 April 2013

A biophysical basis for mucus solids concentration as a candidate biomarker for airways disease

In human airways diseases, including cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), host defense is compromised and airways inflammation and infection often result. Mucus clearance and trapping of inhaled pathogens constitute key elements of host defense. Clearance rates are governed by mucus viscous and elastic moduli at physiological driving frequencies, whereas transport of trapped pathogens in mucus layers is governed by diffusivity. There is a clear need for simple and effective clinical biomarkers of airways disease that correlate with these properties. We tested the hypothesis that mucus solids concentration, indexed as weight percent solids (wt%), is such a biomarker. Passive microbead rheology was employed to determine both diffusive and viscoelastic properties of mucus harvested from human bronchial epithelial (HBE) cultures. Guided by sputum from healthy (1.5–2.5 wt%) and diseased (COPD, CF; 5 wt%) subjects, mucus samples were generated in vitro to mimic in vivo physiology, including intermediate range wt% to represent disease progression. Analyses of microbead datasets showed mucus diffusive properties and viscoelastic moduli scale robustly with wt%. Importantly, prominent changes in both biophysical properties arose at ∼4 wt%, consistent with a gel transition (from a more viscous-dominated solution to a more elastic-dominated gel). These findings have significant implications for: (1) penetration of cilia into the mucus layer and effectiveness of mucus transport; and (2) diffusion vs. immobilization of micro-scale particles relevant to mucus barrier properties. These data provide compelling evidence for mucus solids concentration as a baseline clinical biomarker of mucus barrier and clearance functions.

Development of an advanced intestinal in vitro triple culture permeability model to study transport of nanoparticles

Intestinal epithelial cell culture models, such as Caco-2 cells, are commonly used to assess absorption of drug molecules and transcytosis of nanoparticles across the intestinal mucosa. However, it is known that mucus strongly impacts nanoparticle mobility and that specialized M cells are involved in particulate uptake. Thus, to get a clear understanding of how nanoparticles interact with the intestinal mucosa, in vitro models are necessary that integrate the main cell types. This work aimed at developing an alternative in vitro permeability model based on a triple culture: Caco-2 cells, mucus-secreting goblet cells and M cells. Therefore, Caco-2 cells and mucus-secreting goblet cells were cocultured on Transwells and Raji B cells were added to stimulate differentiation of M cells. The in vitro triple culture model was characterized regarding confluence, integrity, differentiation/expression of M cells and cell surface architecture. Permeability of model drugs and of 50 and 200 nm polystyrene nanoparticles was studied. Data from the in vitro model were compared with ex vivo permeability results (Ussing chambers and porcine intestine) and correlated well. Nanoparticle uptake was size-dependent and strongly impacted by the mucus layer. Moreover, nanoparticle permeability studies clearly demonstrated that particles were capable of penetrating the intestinal barrier mainly via specialized M cells. It can be concluded that goblet cells and M cells strongly impact nanoparticle uptake in the intestine and should thus be integrated in an in vitro permeability model. The presented model will be an efficient tool to study intestinal transcellular uptake of particulate systems.

Ocular Pharmacokinetics of a Novel Loteprednol Etabonate 0.4% Ophthalmic Formulation

Introduction

Topical ophthalmic formulations of corticosteroids are commonly used to treat a variety of ocular diseases and conditions that have an inflammatory component. The purpose of this study was to evaluate the effect of the mucus-penetrating particle (MPP) technology on the pharmacokinetic profile of loteprednol etabonate in the ocular tissues of rabbits.

Methods

Forty-eight New Zealand White rabbits were randomly assigned to two groups (n = 3 rabbits or 6 eyes per time point) and treated with either the novel loteprednol etabonate MPP suspension formulation, 0.4% (LE-MPP 0.4%), or the commercial Lotemax^®-brand loteprednol etabonate ophthalmic suspension, 0.5% (Lotemax 0.5%) (Bausch & Lomb Incorporated, Inc., Rochester, NY, USA). Samples of aqueous humor, various ocular tissues, and plasma were collected from animals over a 12-h period after a single dose of the test articles. Loteprednol etabonate concentrations were assayed using liquid chromatography–tandem mass spectrometry (LC/MS/MS).

Results

Loteprednol etabonate was rapidly absorbed into ocular tissues following administration of either formulation. A higher ocular exposure was achieved using LE-MPP 0.4%, with peak concentrations of approximately threefold higher in ocular tissues and the aqueous humor than Lotemax 0.5%.

Conclusions

Administration of LE-MPP 0.4% improved loteprednol etabonate pharmacokinetic profile in ocular tissues of rabbits. The results of this study support the premise that the MPP technology can be used to enhance ocular exposure for topically applied therapeutic agents. Further studies to assess the clinical efficacy and safety of the LE-MPP formulation are warranted.

Electronic supplementary material

The online version of this article (doi:10.1007/s40123-014-0021-z) contains supplementary material, which is available to authorized users.

The uptake of soluble and particulate antigens by epithelial cells in the mouse small intestine

Intestinal epithelial cells (IECs) overlying the villi play a prominent role in absorption of digested nutrients and establish a barrier that separates the internal milieu from potentially harmful microbial antigens. Several mechanisms by which antigens of dietary and microbial origin enter the body have been identified; however whether IECs play a role in antigen uptake is not known. Using in vivo imaging of the mouse small intestine, we investigated whether epithelial cells (enterocytes) play an active role in the uptake (sampling) of lumen antigens. We found that small molecular weight antigens such as chicken ovalbumin, dextran, and bacterial LPS enter the lamina propria, the loose connective tissue which lies beneath the epithelium via goblet cell associated passageways. However, epithelial cells overlying the villi can internalize particulate antigens such as bacterial cell debris and inert nanoparticles (NPs), which are then found co-localizing with the CD11c+ dendritic cells in the lamina propria. The extent of NP uptake by IECs depends on their size: 20–40 nm NPs are taken up readily, while NPs larger than 100 nm are taken up mainly by the epithelial cells overlying Peyer's patches. Blocking NPs with small proteins or conjugating them with ovalbumin does not inhibit their uptake. However, the uptake of 40 nm NPs can be inhibited when they are administered with an endocytosis inhibitor (chlorpromazine). Delineating the mechanisms of antigen uptake in the gut is essential for understanding how tolerance and immunity to lumen antigens are generated, and for the development of mucosal vaccines and therapies.

Biodistribution and pharmacokinetics of dapivirine-loaded nanoparticles after vaginal delivery in mice

PURPOSE

To assess the potential of polymeric nanoparticles (NPs) to affect the genital distribution and local and systemic pharmacokinetics (PK) of the anti-HIV microbicide drug candidate dapivirine after vaginal delivery.

METHODS

Dapivirine-loaded, poly(ethylene oxide)-coated poly(epsilon-caprolactone) (PEO-PCL) NPs were prepared by a nanoprecipitation method. Genital distribution of NPs and their ability to modify the PK of dapivirine up to 24 h was assessed after vaginal instillation in a female mouse model. Also, the safety of NPs upon daily administration for 14 days was assessed by histological analysis and chemokine/cytokine content in vaginal lavages.

RESULTS

PEO-PCL NPs (180-200 nm) were rapidly eliminated after administration but able to distribute throughout the vagina and lower uterus, and capable of tackling mucus and penetrate the epithelial lining. Nanocarriers modified the PK of dapivirine, with higher drug levels being recovered from vaginal lavages and vaginal/lower uterine tissues as compared to a drug suspension. Systemic drug exposure was reduced when NPs were used. Also, NPs were shown safe upon administration for 14 days.

CONCLUSIONS

Dapivirine-loaded PEO-PCL NPs were able to provide likely favorable genital drug levels, thus attesting the potential value of using this vaginal drug delivery nanosystem in the context of HIV prophylaxis.

Lung gene therapy with highly compacted DNA nanoparticles that overcome the mucus barrier

Inhaled gene carriers must penetrate the highly viscoelastic and adhesive mucus barrier in the airway in order to overcome rapid mucociliary clearance and reach the underlying epithelium; however, even the most widely used viral gene carriers are unable to efficiently do so. We developed two polymeric gene carriers that compact plasmid DNA into small and highly stable nanoparticles with dense polyethylene glycol (PEG) surface coatings. These highly compacted, densely PEG-coated DNA nanoparticles rapidly penetrate human cystic fibrosis (CF) mucus ex vivo and mouse airway mucus ex situ. Intranasal administration of the mucus penetrating DNA nanoparticles greatly enhanced particle distribution, retention and gene transfer in the mouse lung airways compared to conventional gene carriers. Successful delivery of a full-length plasmid encoding the cystic fibrosis transmembrane conductance regulator protein was achieved in the mouse lungs and airway cells, including a primary culture of mucus-covered human airway epithelium grown at air-liquid interface, without causing acute inflammation or toxicity. Highly compacted mucus penetrating DNA nanoparticles hold promise for lung gene therapy.

On the role of specific interactions in the diffusion of nanoparticles in aqueous polymer solutions

Understanding nanoparticle diffusion within non-Newtonian biological and synthetic fluids is essential in designing novel formulations (e.g., nanomedicines for drug delivery, shampoos, lotions, coatings, paints, etc.), but is presently poorly defined. This study reports the diffusion of thiolated and PEGylated silica nanoparticles, characterized by small-angle neutron scattering, in solutions of various water-soluble polymers such as poly(acrylic acid) (PAA), poly(N-vinylpyrrolidone) (PVP), poly(ethylene oxide) (PEO), and hydroxyethylcellulose (HEC) probed using NanoSight nanoparticle tracking analysis. Results show that the diffusivity of nanoparticles is affected by their dimensions, medium viscosity, and, in particular, the specific interactions between nanoparticles and the macromolecules in solution; strong attractive interactions such as hydrogen bonding hamper diffusion. The water-soluble polymers retarded the diffusion of thiolated particles in the order PEO > PVP > PAA > HEC whereas for PEGylated silica particles retardation followed the order PAA > PVP = HEC > PEO. In the absence of specific interactions with the medium, PEGylated nanoparticles exhibit enhanced mobility compared to their thiolated counterparts despite some increase in their dimensions.

Uptake and transport of B12-conjugated nanoparticles in airway epithelium

Non-invasive delivery of biotherapeutics, as an attractive alternative to injections, could potentially be achieved through the mucosal surfaces, utilizing nanoscale therapeutic carriers. However, nanoparticles do not readily cross the mucosal barriers, with the epithelium presenting a major barrier to their translocation. The transcytotic pathway of vitamin B12 has previously been shown to 'ferry' B12-decorated nanoparticles across intestinal epithelial (Caco-2) cells. However, such studies have not been reported for the airway epithelium. Furthermore, the presence in the airways of the cell machinery responsible for transepithelial trafficking of B12 is not widely reported. Using a combination of molecular biology and immunostaining techniques, our work demonstrates that the bronchial cell line, Calu-3, expresses the B12-intrinsic factor receptor, the transcobalamin II receptor and the transcobalamin II carrier protein. Importantly, the work showed that sub-200 nm model nanoparticles chemically conjugated to B12 were internalised and transported across the Calu-3 cell layers, with B12 conjugation not only enhancing cell uptake and transepithelial transport, but also influencing intracellular trafficking. Our work therefore demonstrates that the B12 endocytotic apparatus is not only present in this airway model, but also transports ligand-conjugated nanoparticles across polarised epithelial cells, indicating potential for B12-mediated delivery of nanoscale carriers of biotherapeutics across the airways.

The microstructure and bulk rheology of human cervicovaginal mucus are remarkably resistant to changes in pH

The protective barrier, lubricant, and clearance functions of mucus are intimately coupled to its microstructure and bulk rheology. Mucus gels consist of a network of mucin biopolymers along with lipids, salts, and other proteins and exhibit similar biochemical and physical properties across diverse mucosal surfaces. Nevertheless, mucus is exposed to a broad range of pH values throughout the human body. Protein functions are typically sensitive to small changes in pH, and prior investigations using reconstituted, purified mucin gels suggested mucus undergoes a transition from a low-viscosity liquid at neutral pH to a highly viscoelastic solid at low pH. We sought to determine whether those observations hold for fresh, minimally perturbed human mucus ex vivo by using different-sized muco-inert nanoparticles to probe microstructure and cone-and-plate rheometry to measure bulk rheology. We demonstrate that both the microstructure and bulk rheology of fresh, undiluted, and minimally perturbed cervicovaginal mucus exhibit relatively minor changes from pH 1-2 to 8-9, in marked contrast with the pH sensitivity of purified mucin gels. Our work also suggests additional components in mucus secretions, typically eliminated during mucin purification and reconstitution, may play an important role in maintaining the protective properties of mucus.

Fate of paclitaxel lipid nanocapsules in intestinal mucus in view of their oral delivery

The bioavailability of paclitaxel (Ptx) has previously been improved via its encapsulation in lipid nanocapsules (LNCs). In this work, the interactions between LNCs and intestinal mucus are studied because they are viewed as an important barrier to successful oral delivery. The rheological properties of different batches of pig intestinal mucus were studied under different conditions (the effect of hydration and the presence of LNCs). Fluorescence resonance energy transfer (FRET) was used to study the stability of LNCs in mucus at 37°C for at least 3 hours. Diffusion through 223, 446, and 893 μm mucus layers of 8.4, 16.8, and 42 μg/mL Ptx formulated as Taxol® (Bristol-Myers Squibb, Rueil-Malmaison, France) or encapsulated in LNCs (Ptx-LNCs) were investigated. The effect of the size of the LNCs on their diffusion was also investigated (range, 25–110 nm in diameter). Mucus behaves as a non-Newtonian gel with rheofluidifying properties and a flow threshold. The viscous (G″) and elastic (G′) moduli and flow threshold of the two mucus batches varied with water content, but G′ remained below G″. LNCs had no effect on mucus viscosity and flow threshold. The FRET efficiency remained at 78% after 3 hours. Because the destruction of the LNCs would lead to a FRET efficiency below 25%, these results suggest only a slight modification of LNCs after their contact with mucus. The diffusion of Taxol® and Ptx-LNCs in mucus decreases if the mucus layer is thicker. Interestingly, the apparent permeability across mucus is higher for Ptx-LNCs than for Taxol® for drug concentrations of 16.8 and 42 μg/mL Ptx (P<0.05). The diffusion of Ptx-LNCs through mucus is not size-dependent. This study shows that LNCs are stable in mucus, do not change mucus rheological properties, and improve Ptx diffusion at low concentrations, thus making these systems good candidates for Ptx oral delivery. The study of the physicochemical interaction between the LNC surface and its diffusion in mucus is now envisioned.

Engineering synthetic vaccines using cues from natural immunity

Vaccines aim to protect against or treat diseases through manipulation of the immune response, promoting either immunity or tolerance. In the former case, vaccines generate antibodies and T cells poised to protect against future pathogen encounter or attack diseased cells such as tumours; in the latter case, which is far less developed, vaccines block pathogenic autoreactive T cells and autoantibodies that target self tissue. Enormous challenges remain, however, as a consequence of our incomplete understanding of human immunity. A rapidly growing field of research is the design of vaccines based on synthetic materials to target organs, tissues, cells or intracellular compartments; to co-deliver immunomodulatory signals that control the quality of the immune response; or to act directly as immune regulators. There exists great potential for well-defined materials to further our understanding of immunity. Here we describe recent advances in the design of synthetic materials to direct immune responses, highlighting successes and challenges in prophylactic, therapeutic and tolerance-inducing vaccines.

Biomaterials-based modulation of the immune system

The immune system is traditionally considered from the perspective of defending against bacterial or viral infections. However, foreign materials like implants can also illicit immune responses. These immune responses are mediated by a large number of molecular signals, including cytokines, antibodies and reactive radical species, and cell types, including macrophages, neutrophils, natural killer cells, T-cells, B-cells, and dendritic cells. Most often, these molecular signals lead to the generation of fibrous encapsulation of the biomaterials, thereby shielding the body from these biomaterials. In this review we will focus on two different types of biomaterials: those that actively modulate the immune response, as seen in antigen delivery vehicles for vaccines, and those that illicit relatively small immune response, which are important for implantable materials. The first serves to actively influence the immune response by co-opting certain immune pathways, while the second tries to mimic the properties of the host in an attempt to remain undetected by the immune system. As these are two very different end points, each type of biomaterial has been studied and developed separately and in recent years, many advances have been made in each respective area, which will be highlighted in this review.

Nanotechnology approaches for inhalation treatment of fibrosis

Cystic fibrosis (CF) is an autosomal recessive monogenetic disease that afflicts nearly 70 000 patients worldwide. The mutation results in the accumulation of viscous mucus in multiple organs especially in the lungs, liver and pancreas. High associated morbidity and mortality is caused by CF due to the lack of effective therapies. It is widely accepted that morbidity and mortality caused by CF is primarily due to the respiratory manifestations of the disease. Consequently, several approaches were recently developed for treatment of lung complications of CF. However, the lack of effective methods for delivery and especially targeted delivery of therapeutics specifically to lung tissues and cells limits the efficiency of the therapy. Local pulmonary delivery of therapeutics has two major advantages over systemic application. First, it enhances the accumulation of therapeutics specifically in the lungs and therefore increases the efficiency of the treatment. Second, local lung delivery substantially prevents the penetration of the delivered drug into the systemic circulation limiting adverse side effects of the treatment on other organs and tissues. This review is focused on different approaches to the treatment of respiratory manifestations of CF as well as on methods of pulmonary delivery of therapeutics.

Formulations for Intranasal Delivery of Pharmacological Agents to Combat Brain Disease: A New Opportunity to Tackle GBM?

Despite recent advances in tumor imaging and chemoradiotherapy, the median overall survival of patients diagnosed with glioblastoma multiforme does not exceed 15 months. Infiltration of glioma cells into the brain parenchyma, and the blood-brain barrier are important hurdles to further increase the efficacy of classic therapeutic tools. Local administration methods of therapeutic agents, such as convection enhanced delivery and intracerebral injections, are often associated with adverse events. The intranasal pathway has been proposed as a non-invasive alternative route to deliver therapeutics to the brain. This route will bypass the blood-brain barrier and limit systemic side effects. Upon presentation at the nasal cavity, pharmacological agents reach the brain via the olfactory and trigeminal nerves. Recently, formulations have been developed to further enhance this nose-to-brain transport, mainly with the use of nanoparticles. In this review, the focus will be on formulations of pharmacological agents, which increase the nasal permeation of hydrophilic agents to the brain, improve delivery at a constant and slow release rate, protect therapeutics from degradation along the pathway, increase mucoadhesion, and facilitate overall nasal transport. A mounting body of evidence is accumulating that the underexplored intranasal delivery route might represent a major breakthrough to combat glioblastoma.

Engineered silica nanoparticles act as adjuvants to enhance allergic airway disease in mice

Background

With the increase in production and use of engineered nanoparticles (NP; ≤ 100 nm), safety concerns have risen about the potential health effects of occupational or environmental NP exposure. Results of animal toxicology studies suggest that inhalation of NP may cause pulmonary injury with subsequent acute or chronic inflammation. People with chronic respiratory diseases like asthma or allergic rhinitis may be even more susceptible to toxic effects of inhaled NP. Few studies, however, have investigated adverse effects of inhaled NP that may enhance the development of allergic airway disease.

Methods

We investigated the potential of polyethylene glycol coated amorphous silica NP (SNP; 90 nm diameter) to promote allergic airway disease when co-exposed during sensitization with an allergen. BALB/c mice were sensitized by intranasal instillation with 0.02% ovalbumin (OVA; allergen) or saline (control), and co-exposed to 0, 10, 100, or 400 μg of SNP. OVA-sensitized mice were then challenged intranasally with 0.5% OVA 14 and 15 days after sensitization, and all animals were sacrificed a day after the last OVA challenge. Blood and bronchoalveolar lavage fluid (BALF) were collected, and pulmonary tissue was processed for histopathology and biochemical and molecular analyses.

Results

Co-exposure to SNP during OVA sensitization caused a dose-dependent enhancement of allergic airway disease upon challenge with OVA alone. This adjuvant-like effect was manifested by significantly greater OVA-specific serum IgE, airway eosinophil infiltration, mucous cell metaplasia, and Th2 and Th17 cytokine gene and protein expression, as compared to mice that were sensitized to OVA without SNP. In saline controls, SNP exposure did cause a moderate increase in airway neutrophils at the highest doses.

Conclusions

These results suggest that airway exposure to engineered SNP could enhance allergen sensitization and foster greater manifestation of allergic airway disease upon secondary allergen exposures. Whereas SNP caused innate immune responses at high doses in non-allergic mice, the adjuvant effects of SNP were found at lower doses in allergic mice and were Th2/Th17 related. In conclusion, these findings in mice suggest that individuals exposed to SNP might be more prone to manifest allergic airway disease, due to adjuvant-like properties of SNP.

Enhanced vaginal drug delivery through the use of hypotonic formulations that induce fluid uptake

Mucosal epithelia use osmotic gradients for fluid absorption and secretion. We hypothesized that administration of hypotonic solutions would induce fluid uptake that could be advantageous for rapidly delivering drugs through mucus to the vaginal epithelium. We found that hypotonic formulations markedly increased the rate at which small molecule drugs and mucoinert nanoparticles (mucus-penetrating particles, or MPP), but not conventional mucoadhesive nanoparticles (CP), reached the vaginal epithelial surface in vivo in mice. Additionally, hypotonic formulations greatly enhanced drug and MPP delivery to the entire epithelial surface, including deep into the vaginal folds (rugae) that drugs or MPP in isotonic formulations failed to reach efficiently. However, hypotonic formulations caused unencapsulated "free" drugs to be drawn through the epithelium, reducing vaginal retention. In contrast, hypotonic formulations caused MPP to accumulate rapidly and uniformly on vaginal surfaces, ideally positioned for localized sustained drug delivery. Using a mouse model of vaginal genital herpes (HSV-2) infection, we found that hypotonic delivery of free drug led to improved immediate protection, but diminished longer-term protection. In contrast, as we previously demonstrated, hypotonic delivery of drug via MPP led to better long-term retention and protection in the vagina. Importantly, we demonstrate that slightly hypotonic formulations provided rapid and uniform delivery of MPP to the entire vaginal surface, thus enabling formulations with minimal risk of epithelial toxicity. Hypotonic formulations for vaginal drug delivery via MPP may significantly improve prevention and treatment of reproductive tract diseases and disorders.

Scalable method to produce biodegradable nanoparticles that rapidly penetrate human mucus

Mucus typically traps and rapidly removes foreign particles from the airways, gastrointestinal tract, nasopharynx, female reproductive tract and the surface of the eye. Nanoparticles capable of rapid penetration through mucus can potentially avoid rapid clearance, and open significant opportunities for controlled drug delivery at mucosal surfaces. Here, we report an industrially scalable emulsification method to produce biodegradable mucus-penetrating particles (MPP). The emulsification of diblock copolymers of poly(lactic-co-glycolic acid) and polyethylene glycol (PLGA-PEG) using low molecular weight (MW) emulsifiers forms dense brush PEG coatings on nanoparticles that allow rapid nanoparticle penetration through fresh undiluted human mucus. In comparison, conventional high MW emulsifiers, such as polyvinyl alcohol (PVA), interrupts the PEG coating on nanoparticles, resulting in their immobilization in mucus owing to adhesive interactions with mucus mesh elements. PLGA-PEG nanoparticles with a wide range of PEG MW (1, 2, 5, and 10 kDa), prepared by the emulsification method using low MW emulsifiers, all rapidly penetrated mucus. A range of drugs, from hydrophobic small molecules to hydrophilic large biologics, can be efficiently loaded into biodegradable MPP using the method described. This readily scalable method should facilitate the production of MPP products for mucosal drug delivery, as well as potentially longer-circulating particles following intravenous administration.

Pulmonary drug delivery: from generating aerosols to overcoming biological barriers-therapeutic possibilities and technological challenges

Research in pulmonary drug delivery has focused mainly on new particle or device technologies to improve the aerosol generation and pulmonary deposition of inhaled drugs. Although substantial progress has been made in this respect, no significant advances have been made that would lead pulmonary drug delivery beyond the treatment of some respiratory diseases. One main reason for this stagnation is the still very scarce knowledge about the fate of inhaled drug or carrier particles after deposition in the lungs. Improvement of the aerosol component alone is no longer sufficient for therapeutic success of inhalation drugs; a paradigm shift is needed, with an increased focus on the pulmonary barriers to drug delivery. In this Review, we discuss some pathophysiological disorders that could benefit from better control of the processes after aerosol deposition, and pharmaceutical approaches to achieve improved absorption across the alveolar epithelium, prolonged pulmonary clearance, and targeted delivery to specific cells or tissues.

Transport of nanoparticles in cystic fibrosis sputum and bacterial biofilms by single-particle tracking microscopy

Aim: The aim of this study was to evaluate the effect of the surface functionalization of model nanoparticles on their mobility in bacterial biofilms and cystic fibrosis sputum. Materials & methods: With single-particle tracking microscopy, the mobility of 0.1- and 0.2-µm fluorescent polyethylene glycol (PEG) modified, carboxylate- and N,N-dimethylethylenediamine-modified polystyrene nanospheres were evaluated in fresh cystic fibrosis sputum, as well as Burkholderia multivorans and Pseudomonas aeruginosa biofilms. Results: PEGylation increased the mobility of the particles in sputum and biofilms, while the charged nanospheres were strongly immobilized. However, the transport of the PEGylated nanoparticles was lower in sputum compared with biofilms. Furthermore, the particle transport showed heterogeneity in samples originating from different patients. Conclusion: This study’s data suggest that for future nanocarrier design it will be essential to combine PEGylation with a targeting moiety to ensure sufficient mobility in mucus and a better accumulation of the nanoparticles in the biofilm.

Original submitted 14 February 2012; Revised submitted 24 July 2012; Published online 5 October 2012