Comparative ototoxic potential of hyaluronic acid and methylcellulose

Hyaluronic acid in otology: Its uses, advantages and drawbacks - A review

OBJECTIVES

Review of the literature for studies involving the use of hyaluronic acid (HA) in otology.

METHODS

Pubmed and OvidMedline were searched using a combination of the following words in different variations: hyaluronic acid, hyaluronate, otolaryngology, otology, ear, tympanic membrane, perforation, tympanostomy, tympanoplasty, myringoplasty, packing, middle ear, cochlea, gene delivery, gene therapy, cochlear implant, hearing loss, meniere, vertigo, otitis and cholesteatoma.

RESULTS

The papers relevant for this review were triaged based on abstracts and titles and were then categorized based on topic/disease entity/procedure. The papers were read and summarized in order to use their findings in this review.

CONCLUSIONS

HA is being recently used as adjuvant therapy for multiple inflammatory conditions and in tissue repair. These immunomodulatory properties and biocompatibility have interested researchers specially in the field of otology for repair, gene delivery, immunomodulation etc. Recent data in the field show optimistic results for the use of HA in several conditions especially tympanic membrane perforations and gene delivery. It also establishes the role of HA as ancillary treatment in many other otologic pathologies. This review presents the most recent findings on the use of HA in otology. The results could be used to guide clinical practice and incite further research based on the presented results of the literature.

Controlled drug release to the inner ear: Concepts, materials, mechanisms, and performance

Progress in drug delivery to the ear has been achieved over the last few years. This review illustrates the main mechanisms of controlled drug release and the resulting geometry- and size-dependent release kinetics. The potency, physicochemical properties, and stability of the drug molecules are key parameters for designing the most suitable drug delivery system. The most important drug delivery systems for the inner ear include solid foams, hydrogels, and different nanoscale drug delivery systems (e.g., nanoparticles, liposomes, lipid nanocapsules, polymersomes). Their main characteristics (i.e., general structure and materials) are discussed, with special attention given to underlining the link between the physicochemical properties (e.g., surface areas, glass transition temperature, microviscosity, size, and shape) and release kinetics. An appropriate characterization of the drug, the excipients used, and the formulated drug delivery systems is necessary to achieve a deeper understanding of the release process and decrease variability originating from the drug delivery system. This task cannot be solved by otologists alone. The interdisciplinary cooperation between otology/neurotology, pharmaceutics, physics, and other disciplines will result in improved drug delivery systems for the inner ear.

Recent advances in local drug delivery to the inner ear

Inner ear diseases are not adequately treated by systemic drug administration mainly because of the blood-perilymph barrier that reduces exchanges between plasma and inner ear fluids. Local drug delivery methods including intratympanic and intracochlear administrations are currently developed to treat inner ear disorders more efficiently. Intratympanic administration is minimally invasive but relies on diffusion through middle ear barriers for drug entry into the cochlea, whereas intracochlear administration offers direct access to the colchlea but is rather invasive. A wide range of drug delivery systems or devices were evaluated in research and clinic over the last decade for inner ear applications. In this review, different strategies including medical devices, hydrogels and nanoparticulate systems for intratympanic administration, and cochlear implant coating or advanced medical devices for intracoclear administration were explored with special attention to in vivo studies. This review highlights the promising systems for future clinical applications as well as the current hurdles that remain to be overcome for efficient inner ear therapy.

Repair of tympanic membrane perforation using novel adjuvant therapies: a contemporary review of experimental and tissue engineering studies

OBJECTIVE

To perform a contemporary review of experimental studies to describe the effects of various novel adjuvant therapies in enhancing tympanic membrane (TM) perforation healing.

METHODS

A PubMed search for articles from January 2000 to June 2012 related to TM perforation, along with the references of those articles, was performed. Inclusion and exclusion criteria were applied to all experimental studies assessing adjuvant therapies to TM healing.

RESULTS

Many studies have assessed the efficacy of biomolecules or growth factors, such as epidermal growth factors and basic fibroblast growth factors, in TM regeneration with significant success. More recent strategies in TM tissue engineering have involved utilizing bioengineered scaffold materials, such as silk fibroin, chitosan, calcium alginate, and decellularized extracellular matrices. Most scaffold materials demonstrated biocompatibility and faster TM perforation healing rates.

CONCLUSION

Although several studies have demonstrated promising results, many questions still remain, such as the adequacy of animal models and long-term biocompatibility of adjuvant materials. As well, further studies comparing various adjuvant substances and bioscaffolds are required prior to clinical application.

Safety and efficacy of carbomethylcellulose foam in guinea pig middle ear surgery

OBJECTIVE

Carbomethylcellulose (CMC) foam has been widely adopted to promote hemostasis and healing in sinus surgery. There has been interest in the use of CMC in middle ear surgery. The purpose of this study was to evaluate the safety and efficacy of CMC foam for use in middle ear surgery.

STUDY DESIGN

Prospective, controlled.

SETTING

Academic research laboratory.

SUBJECTS AND METHODS

Adult guinea pigs underwent experimental tympanoplasty followed by packing of the middle ear (n = 19 per group) with CMC, hyaluronic acid (HA), or gelatin sponge (GS). Auditory evoked brainstem response testing and otomicroscopy were performed before and serially for eight weeks after surgery. Tympanic membrane healing, hemostasis, and retention of packing material were assessed.

RESULTS

All tympanic membranes treated with CMC healed by week eight. Less postoperative bleeding was observed with CMC than with HA or GS. Surgery elevated auditory thresholds, at least temporarily, in all groups. However, CMC was associated with greater auditory threshold elevation (15-25 dB) at eight weeks across all test frequencies relative to HA or GS (P < 0.01). Residual CMC and scarring were not found in the middle ear, indicating that the hearing loss was sensorineural. No head tilt posturing suggestive of vestibulopathy was seen.

CONCLUSION

CMC was associated with hearing loss and may be ototoxic. Therefore, CMC should not be used in human middle ears given the presence of several nontoxic alternative materials.

Soft cochlear implantation: rationale for the surgical approach

Recent advances in cochlear implant technology have focused renewed attention on the preservation of residual hearing. The focus on preservation of residual hearing is driven by the concept of electroacoustic stimulation. This option depends on the insertion of a short cochlear implant electrode into the basal region of the cochlea while preserving native function in the apical region. The desire to preserve residual hearing has led to the development of the soft-surgery cochlear implantation technique. Here, the authors evaluate its various components. Avoiding entry of blood into the cochlea and the use of hyaluronate seem to be reasonably supported, whereas the use of topical steroids is unlikely to be beneficial. The site of entry into the cochlea, the use of contoured or straight devices, and the depth of insertion are also evaluated. The authors highlight the importance of systematic recording of outcomes and surgical events.

Functional and morphological effects of fotemustine on the auditory system of the rat

OBJECTIVE

This study aimed to elucidate the potential inner-ear effects of fotemustine, a chemotherapeutic agent which crosses the blood-brain barrier and is used in the treatment of primary and metastatic brain tumours and metastatic melanoma.

METHODS

This study utilised distortion product otoacoustic emissions and transmission electron microscopy in order to conduct electrophysiological and morphological assessments, using a rat experimental model. Twelve ears of six male rats were examined two months following intraperitoneal slow infusion of fotemustine (100 mg/m2 or 7.4 mg/kg). Pre- and post-treatment measurements were compared. Finally, electron microscopy was performed on three rat temporal bones.

RESULTS

After infusion of fotemustine, distortion product otoacoustic emissions revealed a significant reduction in signal-to-noise ratios only at 3600 Hz (from 11.95 +/- 7.52 to -0.26 +/- 9.45 dB) and at 3961 Hz (from 18.09 +/- 7.49 to 6.74 +/- 12.11 dB) (referenced to 2f1 - f2). Transmission electron microscopy of the temporal bone revealed ultrastructural changes in the outer hair cells, stria vascularis and cochlear ganglion at the cochlear basal turn. The ganglion cell perikarya were unaffected.

CONCLUSIONS

Fotemustine was administered via intraperitoneal slow infusion in a rat experimental model. Twelve ears of six survivors, from 10 rats, were evaluated at the second month. Fotemustine was determined to have a potential for ototoxicity at 3600 and 3961 Hz. Three randomly chosen rats underwent electron microscopy for morphological analysis. Morphological effects in the cochlear basal turn were observed. Oedematous intracytoplasmic spaces and perivascular areas of the stria vascularis, as well as distorted chromatin content, were detected, thereby suggesting potential ototoxic effects for this agent. Further experimental and clinical studies are required in order to determine whether the effect seen in this pilot study is reversible, and to analyse effects in humans.

Ultrastructural and electrophysiologic changes of rat cochlea after irradiation

OBJECTIVE/HYPOTHESIS

To determine the acute and subacute cochlear effects of sublethal total body irradiation.

STUDY DESIGN

The study was designed prospectively as a Sprague-Dawley (SD) rat model with otoacoustic emission measurement.

METHODS AND MATERIALS

Ten rats and 20 ears were included in the study. Distortion product otoacoustic emission (DPOAE) measurements were performed under ketamine anesthesia before and 1 to 8 weeks after sublethal dose total body irradiation. Eight and six rats survived at the first and eighth week measurements, respectively. The frequency bandwidth was set to 1,067 Hz (referenced to f1) - 9,512 Hz (referenced to f2) (2f1 - f2 = 832 - 6,076 Hz) and eight points were sampled per octave, but low-frequency (<2,549 Hz [referenced to 2f1 - f2]) results were not included in the analysis. Averages were obtained at each frequency, and statistical analysis was performed to compare the pre-and postradiation values. Then, three of the rats were killed for transient electron microscopy (TEM) of the temporal bones.

RESULTS

The posttreatment DPOAEs at almost all frequencies showed a trend toward decline at both the first and eighth weeks, but significant reduction was only detected at 3,600 and 3,961 Hz (referenced to 2f1 - f2) in the first week. TEM of the cochlea revealed ultrastructural changes in the outer hair cells (OHCs) and stria vascularis of the basal turn. The cochlear ganglion nuclei and cochlear nerve axons were unaffected.

CONCLUSION

Radiation can affect the cochlea in the acute phase at the mid to high frequencies; further prediction for long-term effects requires longer follow-ups.

An animal model based on the Sprague Dawley rat for the evaluation of ototoxicity

Various methodological approaches that can be used to detect ototoxic effects caused by the administration of various substances are presented, using the Sprague-Dawley rat as an animal model. Electrophysiological data are also presented to show how the model behaves with potentially ototoxic (hyaluronic acid) and initially inert (hydroxy-propyl-methyl-cellulose) substances.

Healing large tympanic membrane perforations using hyaluronic acid, basic fibroblast growth factor, and epidermal growth factor

Large tympanic membrane perforations usually require a surgical tympanoplasty for closure. Reducing surgical costs and risks has encouraged investigators to examine nonsurgical office procedures for healing these perforations. Growth accelerators are the most promising agents. We study here the closure of large acute perforations using weekly applications of 1 mg of 1% hyaluronic acid (HA), 0.4 microg basic fibroblast growth factor (bFGF), or 1.0 microg epidermal growth factor (EGF) directly to the tympanic membranes of the experimental ears. Control ears were treated with 0. 1 mL Vasocidin. Complete closure was obtained in 100% of the ears treated with HA and EGF and 85.7% of those treated with bFGF by day 21, compared with 63.6% of the controls by day 32. Moderate-to-severe ipsilateral and contralateral external canal hypertrophy was noted in 14.2% and 37.5% of the ears treated with bFGF and HA, respectively, but was not seen in ears treated with EGF or in the control group.

Hyaluronic acid. A review of its pharmacology and use as a surgical aid in ophthalmology, and its therapeutic potential in joint disease and wound healing

Hyaluronic acid is a naturally occurring polysaccharide with distinct physicochemical properties which underlie its application as a viscoelastic tool in ophthalmological surgery. In cataract surgery the role of hyaluronic acid in facilitating procedures and protecting the corneal endothelium is well established. Some benefit has also been gained with the use of hyaluronic acid in penetrating keratoplasty, trabeculectomy, retinal reattachment and trauma surgery, although its efficacy in these indications is less well-defined in the published literature. In addition to its lubricating and cushioning properties, demonstration of some in vitro anti-inflammatory activity and a possible disease-modifying effect for hyaluronic acid in animals has prompted its investigation as a treatment in osteoarthritis and, to a much lesser extent, in rheumatoid arthritis. Hyaluronic acid 20 mg, as weekly intra-articular injections for 3 to 7 weeks, improved knee pain and joint motion in patients with osteoarthritis. Although this occurred to a greater degree than with placebo in most comparisons, the effects of hyaluronic acid was similar to those of placebo in the largest trial. In the few available comparisons with other agents, hyaluronic acid appeared equivalent to methylprednisolone 40 mg (for 3 weeks) and to a single injection of triamcinolone 40 mg. Hyaluronic acid was distinguished from other therapies by providing a sustained effect after treatment discontinuation. Together with its very good tolerability profile, these properties justify further study of hyaluronic acid in patients with osteoarthritis. Some limited evidence of improvement in patients with rheumatoid arthritis, and a possible healing effect of hyaluronic acid on tympanic membrane perforations, represent additional areas of interest for future investigation. In summary, hyaluronic acid is a well-established adjunct to cataract surgery and may prove to be a promising option in the treatment of patients with osteoarthritis. Its very good tolerability provides further impetus for examination of its potential role in an extended scope of arthritic and ophthalmological indications, and in wound healing.