Optimisation of peptides that actively cross the tympanic membrane by random amino acid extension: a phage display study

Peptide-Mediated Transport Across the Intact Tympanic Membrane Is Intracellular, with the Rate Determined by the Middle Ear Mucosal Epithelium

The tympanic membrane forms an impenetrable barrier between the ear canal and the air-filled middle ear, protecting it from fluid, pathogens, and foreign material entry. We previously screened a phage display library and discovered peptides that mediate transport across the intact membrane. The route by which transport occurs is not certain, but possibilities include paracellular transport through loosened intercellular junctions and transcellular transport through the cells that comprise the various tympanic membrane layers. We used confocal imaging to resolve the phage's path through the membrane. Phages were observed in puncta within the cytoplasm of tympanic membrane cells, with no evidence of phages within junctions between epithelial cells. This result indicates that transport across the membrane is transcellular and within vesicles, consistent with the transcytosis process. The trans-tympanic peptide phages display a wide range of transport efficiencies for unknown reasons. This could include variation in tympanic membrane binding, entry into the membrane, crossing the membrane, or exiting into the middle ear. To address this, we titered phages recovered from within the membrane for phages with differing transport rates. We found that differences in the transport rate were inversely related to their presence within the tympanic membrane. This suggests that differences in the transport rate primarily reflect the efficiency of an exocytotic exit from the mucosal epithelium rather than entry into, or passage across, the membrane.

Transtympanic delivery of V2O5 nanowires with a tympanic-membrane penetrating peptide

Otitis media is a prevalent pediatric condition. Local delivery of antimicrobial agents to treat otitis media is hindered by the low permeability of the stratum corneum layer in the tympanic membrane. While nanozymes, often inorganic nanoparticles, have been developed to cure otitis media in an antibiotic-free manner in a chinchilla animal model, the tympanic membrane creates an impenetrable barrier that prevents the local and non-invasive delivery of nanozymes. Here, we use a newly developed vanadium pentoxide (V2O5) nanowire as an example, which catalyzes the metabolic products of an otitis media pathogen (Streptococcus pneumoniae) into antiseptics, to explore the transtympanic delivery strategies for antimicrobial nanozymes. V2O5 nanowires with smaller dimensions (<300 nm in length) were synthesized by optimizing the synthesis conditions. To enhance penetrations across intact tympanic membranes, the nanowire was mixed or surface-modified with a trans-tympanic peptide, TMT3. The peptide-modified nanowires were characterized for their physical properties, catalytic activities, and antimicrobial activities. The cytotoxicity profile and permeation across ex vivo tympanic membrane samples were analyzed for the mixed and surface-modified nanozyme formulations.

Biomaterials for non-invasive trans-tympanic drug delivery: requirements, recent advances and perspectives

Various non-invasive delivery systems have recently been developed as an alternative to conventional injections. Local transdermal administration represents the most attractive method due to the low systemic side effects, excellent ease of administration, and persistent drug release. The tympanic membrane (TM), a major barrier between the outer and middle ear, has a similar structure of the stratum corneum compared to the surface of the skin. After several attempts, non-invasive trans-tympanic drug delivery has been regarded as a promising option in the treatment of middle and inner ear diseases. The round window membrane (RWM) was a possible non-invasive delivery approach from the middle to inner ear. The improved permeability of nanocarriers crossing the RWM is a current hotspot in therapeutics for inner ear diseases. In this review, we include the latest studies exploring non-invasive trans-tympanic delivery to treat middle and inner ear diseases. Both passive and active delivery systems are described. A summary of the benefits and disadvantages of various delivery systems in clinical practice and production procedures is introduced. Finally, future possible approaches for its effective application as a non-invasive middle and inner ear drug delivery system are characterised.

Applications of the phage display technology in molecular biology, biotechnology and medicine

The phage display technology is based on the presentation of peptide sequences on the surface of virions of bacteriophages. Its development led to creation of sophisticated systems based on the possibility of the presentation of a huge variability of peptides, attached to one of proteins of bacteriophage capsids. The use of such systems allowed for achieving enormous advantages in the processes of selection of bioactive molecules. In fact, the phage display technology has been employed in numerous fields of biotechnology, as diverse as immunological and biomedical applications (in both diagnostics and therapy), the formation of novel materials, and many others. In this paper, contrary to many other review articles which were focussed on either specific display systems or the use of phage display in selected fields, we present a comprehensive overview of various possibilities of applications of this technology. We discuss an usefulness of the phage display technology in various fields of science, medicine and the broad sense of biotechnology. This overview indicates the spread and importance of applications of microbial systems (exemplified by the phage display technology), pointing to the possibility of developing such sophisticated tools when advanced molecular methods are used in microbiological studies, accompanied with understanding of details of structures and functions of microbial entities (bacteriophages in this case).

Overcoming barriers: a review on innovations in drug delivery to the middle and inner ear

Despite significant advances in the development of therapeutics for hearing loss, drug delivery to the middle and inner ear remains a challenge. As conventional oral or intravascular administration are ineffective due to poor bioavailability and impermeability of the blood-labyrinth-barrier, localized delivery is becoming a preferable approach for certain drugs. Even then, localized delivery to the ear precludes continual drug delivery due to the invasive and potentially traumatic procedures required to access the middle and inner ear. To address this, the preclinical development of controlled release therapeutics and drug delivery devices have greatly advanced, with some now showing promise clinically. This review will discuss the existing challenges in drug development for treating the most prevalent and damaging hearing disorders, in particular otitis media, perforation of the tympanic membrane, cholesteatoma and sensorineural hearing loss. We will then address novel developments in drug delivery that address these including novel controlled release therapeutics such as hydrogel and nanotechnology and finally, novel device delivery approaches such as microfluidic systems and cochlear prosthesis-mediated delivery. The aim of this review is to investigate how drugs can reach the middle and inner ear more efficiently and how recent innovations could be applied in aiding drug delivery in certain pathologic contexts.

A transcytotic transport mechanism across the tympanic membrane

Drug treatments for middle ear diseases are currently delivered systemically, or locally after opening the impermeable tympanic membrane (TM). We previously used bacteriophage display to discover novel peptides that are actively transported across the intact TM, with a variety of transport rates. Peptide structures were analyzed for evidence regarding the mechanism for this unexpected transport, which was then tested by the application of chemical inhibitors. Primary sequences indicated that trans-TM peptides share one of two amino acid motifs. Secondary structures revealed that linear configurations associate with higher transport rates than coiled structures. Tertiary analysis indicated that the shared sequence motifs are prominently displayed at the free ends of rapidly transported peptide phage. The shared motifs were evaluated for similarity to known motifs. The highest probability matches were for protein motifs involved in transmembrane transport and exosomes. Overall, structural findings suggest that the shared motifs represent binding sequences. They also implicate transcytosis, a polarized cell transport mechanism consisting of endocytosis, transcellular transport, and exocytosis. Inhibitor studies indicated that macropinocytosis, retrograde transport through Golgi and exocytosis participate in transport across the TM, consistent with transcytosis. This process can be harnessed to noninvasively deliver therapeutics to the middle ear.

Novel Antimicrobial Treatment Strategy Based on Drug Delivery Systems for Acute Otitis Media

Despite tremendous success of pneumococcal conjugated vaccine and antimicrobial treatment by amoxicillin, acute otitis media (AOM) still remains as a great medical concern. Failure of antimicrobial treatment includes several factors. The middle ear cavity is surrounded by bone tissue, which makes it difficult to maintain sufficient concentration of antibiotics. Tympanic membrane of AOM patients thickens and actually becomes a barrier for topical therapy. This review discusses novel antimicrobial treatment strategies based on drug delivery systems (DDS) for AOM. To deliver drugs enough to kill the pathogenic bacteria without systemic side effects, the development of new antimicrobial treatment strategy applying innovative drug DDS has been expected. The sustained-release DDS can achieve sufficient time for antimicrobial concentrations to exceed minimum inhibitory concentration (MIC) for time-dependent antibiotics as well as enough maximum concentration for dose-dependent antibiotics to eradicate causative pathogens in the middle ear. The development of trans-tympanic membranes of DDS, such as hydrogels with chemical permeation enhancers (CPEs), is another attractive strategy. Phage is a promising strategy for developing DDS-based therapies. The DDS formulations enable antimicrobial treatment of AOM by a single dose and thus, an attractive future antimicrobial treatment for AOM.

Molecular Screening Strategy to Identify a Non-invasive Delivery Mechanism for the Treatment of Middle Ear Disorders

Middle ear ailments include a broad range of pathological conditions. Otitis media is the leading middle ear disease of childhood, which incurs significant health care resources in developed countries and, in developing countries, causes significant mortality and morbidity. Recurrent and chronic infections of the middle ear lead to the prolonged presence of inflammatory factors and cellular infiltrates resulting in temporary hearing loss. However, long-term alteration of the middle ear space can pose the risk of permanent damage to the delicate ear structures and cause tissue remodeling. While the etiopathogenesis of middle ear diseases is multifactorial, targeting the biological mechanisms and molecular networks that drive disease development is critical. Yet, a pivotal step in realizing the potential of molecular therapies is the development of methods for local drug delivery, since systemic application risks side effects. Utilizing bacteriophage display in the rat, we discovered rare peptides that are able to transit the intact tympanic membrane from the external canal to the middle ear cavity by an active process. An in vitro assay demonstrated that transport occurs across the tympanic membranes of humans and that the peptides cross the membrane independent of phage. Transport of phage, which is ~900 nm in length, suggests that these peptides could non-invasively deliver drug packages or gene therapy vectors into the middle ear.

Unsolved problems and new medical approaches to otitis media

INTRODUCTION

Otitis media (OM) is a spectrum of infectious and inflammatory diseases that involve the middle ear. It includes acute otitis media (AOM), otitis media with effusion (OME) and chronic suppurative otitis media (CSOM).

AREAS COVERED

This manuscript discusses some of the emerging and unsolved problems regarding OM, and some of the newly developed prophylactic and therapeutic medical measures.

EXPERT OPINION

In recent years, considerable progress in the knowledge of OM physiopathology has been made. However, although extremely common, diseases included under OM have not been adequately studied, and many areas of development, evolution and possible treatments of these pathologies are not defined. It is necessary that these deficiencies be quickly overcome if we want to reduce the total burden of a group of diseases that still have extremely high medical, social and economic relevance.

Panel 3: Genomics, precision medicine and targeted therapies

OBJECTIVE

To review the most recent advances in human and bacterial genomics as applied to pathogenesis and clinical management of otitis media.

DATA SOURCES

PubMed articles published since the last meeting in June 2015 up to June 2019.

REVIEW METHODS

A panel of experts in human and bacterial genomics of otitis media was formed. Each panel member reviewed the literature in their respective fields and wrote draft reviews. The reviews were shared with all panel members, and a merged draft was created. The panel met at the 20th International Symposium on Recent Advances in Otitis Media in June 2019, discussed the review and refined the content. A final draft was made, circulated, and approved by the panel members.

CONCLUSION

Trans-disciplinary approaches applying pan-omic technologies to identify human susceptibility to otitis media and to understand microbial population dynamics, patho-adaptation and virulence mechanisms are crucial to the development of novel, personalized therapeutics and prevention strategies for otitis media.

IMPLICATIONS FOR PRACTICE

In the future otitis media prevention strategies may be augmented by mucosal immunization, combination vaccines targeting multiple pathogens, and modulation of the middle ear microbiome. Both treatment and vaccination may be tailored to an individual's otitis media phenotype as defined by molecular profiles obtained by using rapidly developing techniques in microbial and host genomics.

Panel 1: Biotechnology, biomedical engineering and new models of otitis media

OBJECTIVE

To summarize recently published key articles on the topics of biomedical engineering, biotechnology and new models in relation to otitis media (OM).

DATA SOURCES

Electronic databases: PubMed, Ovid Medline, Cochrane Library and Clinical Evidence (BMJ Publishing).

REVIEW METHODS

Articles on biomedical engineering, biotechnology, material science, mechanical and animal models in OM published between May 2015 and May 2019 were identified and subjected to review. A total of 132 articles were ultimately included.

RESULTS

New imaging technologies for the tympanic membrane (TM) and the middle ear cavity are being developed to assess TM thickness, identify biofilms and differentiate types of middle ear effusions. Artificial intelligence (AI) has been applied to train software programs to diagnose OM with a high degree of certainty. Genetically modified mice models for OM have further investigated what predisposes some individuals to OM and consequent hearing loss. New vaccine candidates protecting against major otopathogens are being explored and developed, especially combined vaccines, targeting more than one pathogen. Transcutaneous vaccination against non-typeable Haemophilus influenzae has been successfully tried in a chinchilla model. In terms of treatment, novel technologies for trans-tympanic drug delivery are entering the clinical domain. Various growth factors and grafting materials aimed at improving healing of TM perforations show promising results in animal models.

CONCLUSION

New technologies and AI applications to improve the diagnosis of OM have shown promise in pre-clinical models and are gradually entering the clinical domain. So are novel vaccines and drug delivery approaches that may allow local treatment of OM.

IMPLICATIONS FOR PRACTICE

New diagnostic methods, potential vaccine candidates and the novel trans-tympanic drug delivery show promising results, but are not yet adapted to clinical use.

Microbial otitis media: recent advancements in treatment, current challenges and opportunities

Otitis media (OM) is a common disease affecting humans, especially paediatric populations. OM refers to inflammation of the middle ear and can be broadly classified into two types, acute and chronic. Bacterial infection is one of the most common causes of OM. Despite the introduction of vaccines, the incidence of OM remains significantly high worldwide. In this mini-review article, we discuss the recent treatment modalities for OM, such as suspension gel, transcutaneous immunization, and intranasal and transtympanic drug delivery, including therapies that are currently undergoing clinical trials. We provide an overview of how these recent advancements in therapeutic strategies can facilitate the circumvention of current treatment challenges involving preadolescence soft palate dysfunction, biofilm formation, tympanic membrane (ear drum) barrier and the attainment of efficacious drug concentrations in the middle ear. While traditional first-line immunization strategies are generally not very efficacious against biofilms, new technologies that use transdermal or intranasal drug delivery via chitosan-PsaA nanoparticles have shown promising results in experimental animal models of OM. Sustained drug delivery systems such as penta-block copolymer poloxamer 407-polybutylphosphoester (P407-PBP) or poloxamer 407 (e.g. OTO-201, with the brand name 'OTIPRIO') have demonstrated that treatments can be reduced to a single topical application. The emergence of effective new treatment modalities opens up promising new avenues for the treatment of OM that could lead to improved quality of life for many children and their families.