Cochlear implant surgery facilitates intracochlear distribution of perioperative systemic steroids.

BACKGROUND: Systemically administered steroids are widely utilised for hearing preservation therapies. More recently, steroids have been administered to achieve hearing protection after cochlear implant surgery. Currently there is a lack of understanding as to which administration route offers most therapeutic efficacy, local or systemic administration. Paramount to this are observations in animal studies that systemic administration following implantation offers hearing protection and reduced cochlear fibrosis, despite observations that perilymphatic levels are up to 10-fold higher after local administration in non-implanted cochleae. AIMS/OBJECTIVES: This paper explores the impact that cochlear implantation and associated acute inflammation has on steroid distribution and uptake following systemic administration of dexamethasone. MATERIAL AND METHODS: Eight guinea pigs received systemic dexamethasone 60 min prior to cochlear implantation. Implanted and contralateral non-implanted cochlea were harvested for tissue immunohistochemistry and detection of dexamethasone. RESULTS: Cochleostomy with scala tympani implantation resulted in a significant increase in cochlear dexamethasone signal. This was most notable at the organ of Corti, stria vascularis, and blood product in the scala tympani. CONCLUSIONS AND SIGNIFICANCE: This study demonstrates that the inner ear distribution of systemically administered steroids is enhanced following surgery for cochlear implantation and provides rationale for systemic perioperative steroids in hearing preservation surgery.

Spironolactone Ameliorates Cochlear Implant Induced Endolymphatic Hydrops.

BACKGROUND: Endolymphatic hydrops (EH) has been observed in both animal and human cochleae following cochlear implant (CI) surgery. We tested whether EH could be eliminated by administration of mineralocorticoid steroid antagonist spironolactone and explored the electrophysiological consequences of this. METHODS: Sixty-four adult guinea pigs underwent cochlear implantation with a dummy electrode. Animals then survived either 2, 7, or 28 days. Auditory function was monitored by recording electrocochleography from the round window membrane preimplantation, and on the last day of the experiment. Spironolactone or control solution was added to animals' feed for 7 days (if they survived that long) beginning immediately prior to surgery. The presence of EH was determined using thin-sheet laser imaging microscopy. RESULTS: Treatment with spironolactone resulted in significant reduction in EH in the second cochlear turn 7 days postimplantation. In all animals, the compound action potential (CAP) threshold was elevated 2 days postimplantation, but for most frequencies had recovered substantially by 28 days. There was no treatment effect on CAP thresholds. SP/AP ratios were elevated at day 2. The amplitude growth of the CAP did not differ between test and control groups at any time after implantation. CONCLUSIONS: EH can be suppressed by antagonism of mineralocorticoid receptors in the week after cochlear implantation. Reduction in EH did not lead to any change in hearing, and there was no indication of synaptopathy signalled by reduced CAP amplitude at high sound intensities. We found no electrophysiological evidence that EH early after implantation impacts negatively upon preservation of residual hearing.

Four-point impedance as a biomarker for bleeding during cochlear implantation.

Cochlear implantation has successfully restored the perception of hearing for nearly 200 thousand profoundly deaf adults and children. More recently, implant candidature has expanded to include those with considerable natural hearing which, when preserved, provides an improved hearing experience in noisy environments. But more than half of these patients lose this natural hearing soon after implantation. To reduce this burden, biosensing technologies are emerging that provide feedback on the quality of surgery. Here we report clinical findings on a new intra-operative measurement of electrical impedance (4-point impedance) which, when elevated, is associated with high rates of post-operative hearing loss and vestibular dysfunction. In vivo and in vitro data presented suggest that elevated 4-point impedance is likely due to the presence of blood within the cochlea rather than its geometry. Four-point impedance is a new marker for the detection of cochlear injury causing bleeding, that may be incorporated into intraoperative monitoring protocols during CI surgery.

Intracochlear tPA infusion may reduce fibrosis caused by cochlear implantation surgery.

BACKGROUND: Experiments show that the extent of ongoing fibrotic change within the cochlea can be determined by the volume and pattern of bleeding within the first 24 h following cochlear implantation. Tissue-type plasminogen activator (tPA) is effective at reducing thrombus volume when administered both within and external to the systemic circulation. AIMS/OBJECTIVES: To determine if tPA delivered into the scala tympani immediately following implantation will reduce thrombus volume within the lower basal turn of the cochlea. MATERIALS AND METHODS: Guinea pigs were implanted with either 'soft' or 'hard' arrays and administered tPA or saline via an intra-cochlear infusion immediately after implantation. Hearing was checked prior to, and 2 weeks after implantation. Cochleae were then harvested and imaged. RESULTS: Animals implanted with 'soft' arrays had 4.2% less tissue response compared with animals implanted with 'hard' arrays. In animals receiving 'soft' arrays, tPA reduced the volume of tissue response (measured by the percentage of the lower basal turn of the scala tympani occupied by tissue response) compared with saline. CONCLUSIONS AND SIGNIFICANCE: tPA may be effective in reducing the overall volume of tissue response in routine 'soft' cochlear implantation and may have a greater effect in the event of significant surgical trauma.

Electrode Impedance Fluctuations as a Biomarker for Inner Ear Pathology After Cochlear Implantation.

OBJECTIVES/HYPOTHESIS: Cochlear implant surgery now aims to preserve residual low frequency hearing. The current research explores whether fluctuations in the electrical impedance of cochlear implant electrodes may act as a biomarker for pathological changes that lead to the delayed loss of residual hearing. STUDY DESIGN: Secondary analysis of a double-blinded randomized trial, where methylprednisolone was administered intravenously before cochlear implantation with a view to preserving residual hearing. METHODS: Seventy-four patients with residual hearing after cochlear implant surgery were investigated for an impedance "spike," defined as a median rise of ≥4 kΩ across all electrodes from the baseline measurements. Spikes were related to objective and subjective hearing loss, dizziness, and tinnitus. RESULTS: An impedance spike occurred in 14% (10/74) of enrolled patients. Three months after surgery, five patients exhibited spikes and three of these patients had a total loss of their residual hearing. 4.3% of the 69 patients without spikes lost residual hearing. At 1 year, 9 of 10 patients who exhibited spikes had lost all their residual hearing. 8.1% of the 37 patients who did not experience a spike lost their residual hearing. Seventy percent of patients exhibiting a spike also experienced vertigo. The administration of steroids at the time of surgery did not influence the occurrence of spikes. CONCLUSION: Our results suggest that there is a relationship between a spike and the loss of residual hearing. It seems that rises in impedance can reflect pathology within the inner ear and predict the future loss of residual hearing.

The Role of Preoperative Steroids in Atraumatic Cochlear Implantation Surgery.

HYPOTHESIS: Depth of insertion is related to the extent of tissue response and low frequency hearing loss. Intravenous steroids have greatest effect in reducing postimplantation fibrosis and hearing loss in the presence of significant electrode insertion trauma, when compared with saline treatment. BACKGROUND: Experiments exploring the enhancement of cochlear implantation (CI) outcomes with glucocorticosteroids have produced mixed results, possibly due to lack of standardization of the CI model. METHODS: Forty-eight normal-hearing guinea pigs were randomly implanted with a highly flexible electrode to a depth of 1.5, 3.0, or 5.0 mm. For each insertion depth, sub-cohorts received either intravenous saline ("saline") or dexamethasone ("steroid") 60 minutes before implantation. Shifts in electrocochleography thresholds at 2 to 32 kHz were determined before and 4 weeks after implantation. Cochleae were harvested and imaged. RESULTS: Low-frequency hearing loss was greatest with 5.0 mm insertions. Fracture of the osseous spiral lamina and/or fibrotic involvement of the round window membrane exacerbated hearing loss. The extent of intracochlear fibrosis was directly related to the depth of insertion. Steroids reduced the intracochlear tissue response for deepest insertions and in apical regions of the cochlea where basilar membrane contact was prevalent. Steroids preserved no more hearing than saline at all insertion depths. CONCLUSION: Cochlear trauma influenced postimplantation hearing loss and steroid effect on fibrosis. Fibrosis, and to a lesser extent, postimplantation hearing loss increased proportionally to the depth of insertion. Steroids did not influence fibrosis relating to the cochleostomy, but could reduce scarring as the electrode negotiated the hook region or near the electrode tip.

Defining the Hook Region Anatomy of the Guinea Pig Cochlea for Modeling of Inner Ear Surgery.

HYPOTHESIS: The aim of this study was to describe the hook region anatomy of the guinea pig cochlea to identify the optimal surgical approach for cochlear implantation and to determine what anatomical structures are at risk. BACKGROUND: Animal studies investigating hearing loss after cochlear implantation surgery are currently constrained by the lack of a reproducible implantation model. METHODS: Guinea pig cochleae were imaged using thin-sheet laser imaging microscopy. Images were stitched, reconstructed, and segmented for analysis. Insertion vectors were determined by tracing their paths to the outer wall and converting to Cartesian coordinates. Spherical surface and multiplane views were generated to analyze outer wall and radial forces of the insertion vector. RESULTS: Thin-sheet laser imaging microscopy enabled quantitative, whole specimen analysis of the soft and bony tissue relationships of the complex cochlear hook region in any desired plane without loss of image quality. Round window or cochleostomy approaches in the anteroinferior plane avoided direct damage to cochlear structures. Cochleostomy approach had large interindividual variability of angular depth and outer wall forces but predictable radial force. CONCLUSION: The guinea pig hook region and lower basal turn have similar structural relationships to humans. Careful cochleostomy placement is essentially for minimizing cochlear trauma and for ensuring a straight insertion vector that successfully advances around the outer wall. Experiments with guinea pigs that control for the surgical approach are likely to provide useful insights into the aetiology and the development of therapies directed at postimplantation hearing loss.

The Effect of Round Window Sealants on Delayed Hearing Loss in a Guinea Pig Model of Cochlear Implantation.

AIM: To determine whether the type of material used to seal the cochlea after round window cochlear implantation influences delayed hearing loss. BACKGROUND: Cochlear implants are now prescribed to patients with residual, low-frequency hearing. This hearing-which provides perceptual benefits for the implanted ear-is frequently lost for unknown reasons weeks to months after surgery in a proportion of patients. A post-surgical change in cochlear mechanics, related to the material used to seal the cochlea after round window implantation, may contribute to this loss. METHODS: An electrode array was implanted in guinea pigs via the round window, which was then sealed with muscle, periosteum, or fibrin glue. Auditory brainstem responses (ABRs) to pure tones (2, 8, 16, 24, and 32 kHz) were recorded before surgery and 1, 4, and 12 weeks after surgery, with subjects then euthanized and their cochleae harvested for histological analysis. RESULTS: Muscle and periosteum, but not fibrin glue, exhibited delayed threshold rises at 2 kHz. Twelve weeks after implantation, 2 kHz threshold shifts differed significantly between muscle (mean, 27.1 dB) and fibrin glue (9.3 dB), but not between these groups and periosteum (19.3 dB). Muscle was sometimes associated with much greater tissue reactions than the other sealants. Most cochleae had injuries to the basilar membrane and/or osseous spiral lamina, regardless of sealant. Hair cell counts did not differ significantly among sealants. CONCLUSION: Delayed, low-frequency hearing loss was observed when cochleae were sealed with muscle or periosteum, but not when cochleae were sealed with fibrin glue.

Effect of both local and systemically administered dexamethasone on long-term hearing and tissue response in a Guinea pig model of cochlear implantation.

Dexamethasone administered prior to cochlear implantation has been shown to reduce the loss of residual hearing in experimental settings. However, its effect on the tissue response around the implant has not been extensively studied. In this study dexamethasone sodium phosphate was administered to guinea pigs via local delivery to the round window (2% dexamethasone for 120 min prior to surgery, 'local 2/120', or 20% dexamethasone for 30 min prior to surgery) or intravenously (2 mg/kg dexamethasone for 60 min) prior to implantation. Auditory brainstem responses (ABR) were monitored for 3 months, after which the cochleae were embedded in Spurr's resin and sectioned. The extent of the tissue response and the survival of the neurosensory structures were analysed. Both local 2/120 and systemically delivered dexamethasone improved ABR thresholds when compared with control animals. Systemic dexamethasone also reduced the tissue response around the electrode. This suggests that whilst both locally and systemically administered dexamethasone can protect residual hearing after cochlear implantation, their effects upon the tissue response to implantation may differ.

Early cochlear response and ICAM-1 expression to cochlear implantation.

AIM: To examine the early cochlear response and intercellular cell adhesion molecule-1 (ICAM-1) expression to implantation of a cochlear electrode into the scala tympani. BACKGROUND: Understanding the early response of the cochlea to implantation may inform the duration which drug therapies should be delivered to protect hearing. METHODS: Guinea pigs were implanted with a cochlear electrode and survived 1, 2, or 7 days before they were euthanized, cochleae harvested, processed, and cryosectioned for light microscopy or ICAM-1 immunohistochemistry. RESULTS: On hematoxylin and eosin staining, scala tympani was characterized by the presence of fibrin and blood clot at 1 to 2 days after surgery, with a leukocytic infiltrate, primarily of neutrophils and macrophage-like cells. By 7 days after surgery, fibroblasts had infiltrated the clot, and the numbers of red blood cells (RBCs) and neutrophils had diminished. ICAM-1 expression was greatest in the lateral cochlear wall with highest expression found in the basal turn in the region of the electrode at 24 hours postimplantation. CONCLUSION: The cochlear vasculature is maximally primed to recruit cells from the circulation, as evidenced by ICAM-1 expression levels, at 24 hours after cochlear implantation. This response is similar to that seen after other types of injury. Where cochlear implantation differs is the predominance of fibrin and clot early after electrode insertion before infiltration by fibroblasts by the end of the first postoperative week. These results suggest that anti-inflammatory drugs aimed at reducing the extravasation of immunecompetent cells into the cochlea must be effective over the first few days after surgery. Whether this can be achieved through preoperative treatment alone, or whether therapy will need to continue postoperatively, awaits further experimentation.

How should we best estimate the mean recency duration for the BED method?

BED estimates of HIV incidence from cross-sectional surveys are obtained by restricting, to fixed time T, the period over which incidence is estimated. The appropriate mean recency duration (Ω(T)) then refers to the time where BED optical density (OD) is less than a pre-set cut-off C, given the patient has been HIV positive for at most time T. Five methods, tested using data for postpartum women in Zimbabwe, provided similar estimates of Ω(T) for C = 0.8: i) The ratio (r/s) of the number of BED-recent infections to all seroconversions over T = 365 days: 192 days [95% CI 168-216]. ii) Linear mixed modeling (LMM): 191 days [95% CI 174-208]. iii) Non-linear mixed modeling (NLMM): 196 days [95% CrI 188-204]. iv) Survival analysis (SA): 192 days [95% CI 168-216]. Graphical analysis: 193 days. NLMM estimates of Ω(T)--based on a biologically more appropriate functional relationship than LMM--resulted in best fits to OD data, the smallest variance in estimates of VT, and best correspondence between BED and follow-up estimates of HIV incidence, for the same subjects over the same time period. SA and NLMM produced very similar estimates of Ω(T) but the coefficient of variation of the former was .3 times as high. The r/s method requires uniformly distributed seroconversion events but is useful if data are available only from a single follow-up. The graphical method produces the most variable results, involves unsound methodology and should not be used to provide estimates of Ω(T). False-recent rates increased as a quadratic function of C: for incidence estimation C should thus be chosen as small as possible, consistent with an adequate resultant number of recent cases, and accurate estimation of Ω(T). Inaccuracies in the estimation of Ω(T) should not now provide an impediment to incidence estimation.

An enzyme-initiated Smiles rearrangement enables the development of an assay of MshB, the GlcNAc-Ins deacetylase of mycothiol biosynthesis.

MshB is the N-acetyl-1-D-myo-inosityl-2-amino-2-deoxy-D-glucopyranoside (GlcNAc-Ins) deacetylase active as one of the enzymes involved in the biosynthesis of mycothiol (MSH), a protective low molecular weight thiol present only in Mycobacterium tuberculosis and other actinomycetes. In this study, structural analogues of GlcNAc-Ins in which the inosityl moiety is replaced by a chromophore were synthesized and evaluated as alternate substrates of MshB, with the goal of identifying a compound that would be useful in high-throughput assays of the enzyme. In an unexpected and surprising finding one of the GlcNAc-Ins analogues is shown to undergo a Smiles rearrangement upon MshB-mediated deacetylation, uncovering a free thiol group. We demonstrate that this chemistry can be exploited for the development of the first continuous assay of MshB activity based on the detection of thiol formation by DTNB (Ellman's reagent); such an assay should be ideally suited for the identification of MshB inhibitors by means of high-throughput screens in microplates.

Round window delivery of dexamethasone ameliorates local and remote hearing loss produced by cochlear implantation into the second turn of the guinea pig cochlea.

Application of dexamethasone to the round window has been shown to ameliorate high frequency hearing loss resulting from the trauma of cochlear implantation in experimental animals, but elucidation of the factors influencing protection of the high frequencies has been confounded by the local trauma from electrode array insertion. In this experiment, a second turn cochleostomy and implantation was performed on guinea pigs, to examine protection in the basal turn without the confounding effect of local trauma, as well as to test the efficacy of hearing protection in the second cochlear turn. The implantation resulted in an increase in hearing thresholds across all frequencies examined (2-32 kHz). Local delivery of dexamethasone to the round window prior to implantation protected hearing across frequencies from 2 to 32 kHz. Auditory thresholds improved over the first week after surgery, and then remained stable for the month of the experiment. The protection of hearing in the basal turn increased with longer periods of drug application prior to implantation. The level of hearing protection in the second turn was similar irrespective of the time that the drug was applied, but was greater when a higher steroid concentration was used. It was concluded that steroids protect hearing in the basal turn of the cochlea even when there was no local trauma. The level of hearing protection in the second turn exceeded that expected from models of steroid diffusion through the cochlea, suggesting that inner ear surgery alters the distribution of dexamethasone within the cochlea.

Binding a heparin derived disaccharide to defensin inspired peptides: insights to antimicrobial inhibition from gas-phase measurements.

Due to the ubiquitous presence of polysaccharide moieties on bacterial surfaces, it is hypothesised that a peptide-saccharide interaction plays a key role during the recognition of invading microorganisms by beta-defensins. We have employed different gas-phase methods to investigate these interactions. This manuscript describes: an MS-based titration assay measuring the gas-phase binding of ten beta-defensin related peptides to a sulfated disaccharide derived from heparin (HDD); ion mobility-mass spectrometry-determined collision cross sections of 3 peptides (both free and binding HDD); and results from molecular modelling with the aim of reconciling some of our experimental observations. We observe a clear qualitative correlation between the antimicrobial activity of several beta-defensins and related peptides and their gas-phase binding to a heparin-derived disaccharide (HDD). Four of the ten peptides show >100 micromolar K(d) values with HDD, and no bacteriocidal activity, illustrating that HDD binding correlates with peptide antimicrobial activity. For five of the remaining six peptides, bacteriocidal activity was re-measured with HDD present. For the peptides containing intramolecular disulfide bonds in two out of five, bacteriocidal activity was reduced approximately 10-fold; for the remaining three peptides, which lack intramolecular disulfide bonds, HDD addition had little effect on bacteriocidal activity. The latter results are suggested to arise from the greater degree of flexibility imparted by the removal of disulfide bonds giving the peptides the ability to envelope HDD and assume a "defensin-like" fold. Thus gas-phase analysis is put forward as a powerful tool for assessing the properties of antimicrobial peptides providing valuable insights in the mechanism of antimicrobial inhibition.

Permanent and transient effects of locally delivered n-acetyl cysteine in a guinea pig model of cochlear implantation.

Protection of residual hearing after cochlear implant surgery can improve the speech and music perception of cochlear implant recipients, particularly in the presence of background noise. Surgical trauma and chronic inflammation are thought to be responsible for a significant proportion of residual hearing loss after surgery. Local delivery of the anti-oxidant precursor n-acetyl cysteine (NAC) to the cochlea via round window 30min prior to surgery, increased the level of residual hearing at 24-32kHz 4weeks post surgery compared to controls. The hearing protection was found in the basal turn near the site of implantation. Coincidentally, the basal turn was also the location that sustained the greatest hearing loss. As well as protecting residual hearing, NAC-treated animals demonstrated a reduction in the chronic inflammatory changes associated with implantation. While these findings indicate that anti-oxidant therapy can be used to reduce the hearing loss associated with surgical trauma, the local delivery of NAC was associated with a transient increase in hearing thresholds, and osseoneogenesis was seen in a greater number of NAC-treated animals. These side-effects would limit its clinical use through local cochlear administration. However, it is not known yet whether these effects would also be produced by other anti-oxidants, or ameliorated by using a different route of administration.

Targeted therapy of the inner ear.

BACKGROUND: There is experimental evidence that targeted delivery of steroids to the inner ear can protect hearing during cochlear implant surgery. The best protection appears to be achieved through pre-treatment of the cochlea, but the time period required for treatment is long compared with the duration of surgery, and needs further optimization. The stability of hearing thresholds is determined over a 3-month period after hearing preservation cochlear implantation. METHODS: Adult guinea pigs were implanted with a miniature cochlear implant electrode, and pure tone auditory brainstem response (ABR) thresholds were estimated in response to pure tones of 2-32 kHz immediately after surgery and at 1 week, 1 month and 3 months. Spiral ganglion cell (SGC) densities were estimated from mid-modular histological sections of the cochlea. Thirty minutes prior to implantation, a polymeric sponge (Seprapack, Genzyme) was loaded with either a 2% solution of dexamethasone phosphate or normal saline (control) and placed onto the round window. RESULTS: Implantation was associated with an immediate elevation in thresholds across frequencies, with a full recovery below 2 kHz over the next week and a partial recovery of thresholds at higher frequencies. These thresholds remained unchanged for the next 3 months. There was an immediate and sustained reduction in the elevation of thresholds at 32 kHz in dexamethasone-treated animals. SGC densities were greater in steroid-treated animals than controls in the basal turn of the cochlea (at the region of implantation) 3 months after implantation. CONCLUSION: It is concluded that ABR thresholds remain stable for 3 months after cochlear implantation in the guinea pig, and that local application of steroids to the inner ear prior to implantation is an effective method of preserving SGC populations when there is residual hearing at the time of implantation.

Factors influencing the efficacy of round window dexamethasone protection of residual hearing post-cochlear implant surgery.

AIM: To protect hearing in an experimental model of cochlear implantation by the application of dexamethasone to the round window prior to surgery. The present study examined the dosage and timing relationships required to optimise the hearing protection. METHODS: Dexamethasone or saline (control) was absorbed into a pledget of the carboxymethylcellulose and hyaluronic acid and applied to the round window of the guinea pig prior to cochlear implantation. The treatment groups were 2% w/v dexamethasone for 30, 60 and 120min; 20% dexamethasone applied for 30min. Auditory sensitivity was determined pre-operatively, and at 1 week after surgery, with pure-tone auditory brainstem response audiometry (2-32kHz). Cochlear implantation was performed via a cochleostomy drilled into the basal turn of the cochlea, into which a miniature cochlear implant dummy electrode was inserted using soft-surgery techniques. RESULTS: ABR thresholds were elevated after cochlear implantation, maximally at 32kHz and to a lesser extent at lower frequencies. Thresholds were less elevated after dexamethasone treatment, and the hearing protection improved when 2% dexamethasone was applied to the round window for longer periods of time prior to implantation. The time that dexamethasone need be applied to achieve hearing protection could be reduced by increasing the concentration of steroid, with a 20% application for 30min achieving similar levels of protection to a 60min application of 2% dexamethasone. CONCLUSIONS: Hearing protection is improved by increasing the time that dexamethasone is applied to the round window prior to cochlear implantation, and the waiting time can be reduced by increasing the steroid concentration. These results suggest that the diffusion dexamethasone through the cochlea is the prime determinant of the extent of hearing protection.

Development of an ion mobility quadrupole time of flight mass spectrometer.

We describe here a new ion mobility capable mass spectrometer which comprises a drift cell for mobility separation and a quadrapole time of flight mass spectrometer for mass analysis--the MoQTOF. A commercial QToF instrument (Micromass UK Ltd., Manchester, UK) has been modified by the inclusion of an additional chamber containing a drift cell and ancillary ion optics. The drift cell is 5.1 cm long made from a copper block and is mounted from a top hat flange in a chamber situated post source optics and prior to the quadapole analyzer. Details of this instrument are provided along with information about how it can be used to acquire mobilities of ions along with their mass to charge ratios. The MoQTOF is used to examine conformations of a series of antimicrobial peptides based on a beta-defensin template. In vivo, these cationic cystine-rich amphiphilic peptides are conformationally restrained by three or more disulfide bridges, although recent findings by several groups have cast doubt on the importance of canonical disulfide pairing to antimicrobial activities. By synthesizing a panel of variants to Defb14 (the murine orthologue of HBD3), we exploit ion mobility to distinguish conformational differences which arise due to disulfide formation and to the hydrophobicity of the peptide sequence. Our gas-phase results are interpreted in terms of the antimicrobial and chemotacic properties of beta-defensins, and this mass spectrometry based approach to discern structure may have a role in future design of novel antibiotics.

Effects of round window dexamethasone on residual hearing in a Guinea pig model of cochlear implantation.

UNLABELLED: To study electric acoustic stimulation, we have developed a model of guinea pig cochlear implantation via a cochleostomy. Thirty minutes prior to implantation, a hyaluronic acid/carboxymethylcellulose bead, loaded with either dexamethasone or normal saline, was placed upon the round window membrane. Animals that did not receive beads acted as controls. Pure-tone auditory brainstem response thresholds were estimated before and after electrode insertion, and 1 and 4 weeks later. Selected cochlear histology was performed. RESULTS: Dexamethasone could be detected in the cochlea for 24 h after cochlear implantation. Thresholds were elevated across frequencies in all animals immediately after surgery. These thresholds recovered completely at and below 2 kHz, and partially at higher frequencies by 1 week after implantation. At 32 kHz, but not the lower frequencies, the presence of dexamethasone had a significant protective effect upon hearing, which increased in magnitude over time. The protection was greatest in difficult implantations where an intractable resistance to electrode insertion was met. There was a persistent foreign body reaction at the site of implantation of saline-treated implanted ears but not in the dexamethasone-treated implanted ears. CONCLUSION: Short-term preoperative delivery of dexamethasone through the round window can protect residual hearing during cochlear implantation, especially during technically difficult surgery.

The complexity of selection at the major primate beta-defensin locus.

BACKGROUND: We have examined the evolution of the genes at the major human beta-defensin locus and the orthologous loci in a range of other primates and mouse. For the first time these data allow us to examine selective episodes in the more recent evolutionary history of this locus as well as the ancient past. We have used a combination of maximum likelihood based tests and a maximum parsimony based sliding window approach to give a detailed view of the varying modes of selection operating at this locus. RESULTS: We provide evidence for strong positive selection soon after the duplication of these genes within an ancestral mammalian genome. Consequently variable selective pressures have acted on beta-defensin genes in different evolutionary lineages, with episodes both of negative, and more rarely positive selection, during the divergence of primates. Positive selection appears to have been more common in the rodent lineage, accompanying the birth of novel, rodent-specific beta-defensin genes. These observations allow a fuller understanding of the evolution of mammalian innate immunity. In both the rodent and primate lineages, sites in the second exon have been subject to positive selection and by implication are important in functional diversity. A small number of sites in the mature human peptides were found to have undergone repeated episodes of selection in different primate lineages. Particular sites were consistently implicated by multiple methods at positions throughout the mature peptides. These sites are clustered at positions predicted to be important for the specificity of the antimicrobial or chemoattractant properties of beta-defensins. Surprisingly, sites within the prepropeptide region were also implicated as being subject to significant positive selection, suggesting previously unappreciated functional significance for this region. CONCLUSIONS: Identification of these putatively functional sites has important implications for our understanding of beta-defensin function and for novel antibiotic design.