Dual Drug Delivery in Cochlear Implants: In Vivo Study of Dexamethasone Combined with Diclofenac or Immunophilin Inhibitor MM284 in Guinea Pigs.

Cochlear implants are well established to treat severe hearing impairments. Despite many different approaches to reduce the formation of connective tissue after electrode insertion and to keep electrical impedances low, results are not yet satisfying. Therefore, the aim of the current study was to combine the incorporation of 5% dexamethasone in the silicone body of the electrode array with an additional polymeric coating releasing diclofenac or the immunophilin inhibitor MM284, some anti-inflammatory substances not yet tested in the inner ear. Guinea pigs were implanted for four weeks and hearing thresholds were determined before implantation and after the observation time. Impedances were monitored over time and, finally, connective tissue and the survival of spiral ganglion neurons (SGNs) were quantified. Impedances increased in all groups to a similar extent but this increase was delayed in the groups with an additional release of diclofenac or MM284. Using Poly-L-lactide (PLLA)-coated electrodes, the damage caused during insertion was much higher than without the coating. Only in these groups, connective tissue could extend to the apex of the cochlea. Despite this, numbers of SGNs were only reduced in PLLA and PLLA plus diclofenac groups. Even though the polymeric coating was not flexible enough, MM284 seems to especially have potential for further evaluation in connection with cochlear implantation.

A PLLA Coating Does Not Affect the Insertion Pressure or Frictional Behavior of a CI Electrode Array at Higher Insertion Speeds.

To prevent endocochlear insertion trauma, the development of drug delivery coatings in the field of CI electrodes has become an increasing focus of research. However, so far, the effect of a polymer coating of PLLA on the mechanical properties, such as the insertion pressure and friction of an electrode array, has not been investigated. In this study, the insertion pressure of a PLLA-coated, 31.5-mm long standard electrode array was examined during placement in a linear cochlear model. Additionally, the friction coefficients between a PLLA-coated electrode array and a tissue simulating the endocochlear lining were acquired. All data were obtained at different insertion speeds (0.1, 0.5, 1.0, 1.5, and 2.0 mm/s) and compared with those of an uncoated electrode array. It was shown that both the maximum insertion pressure generated in the linear model and the friction coefficient of the PLLA-coated electrode did not depend on the insertion speed. At higher insertion speeds above 1.0 mm/s, the insertion pressure (1.268 ± 0.032 mmHg) and the friction coefficient (0.40 ± 0.15) of the coated electrode array were similar to those of an uncoated array (1.252 ± 0.034 mmHg and 0.36 ± 0.15). The present study reveals that a PLLA coating on cochlear electrode arrays has a negligible effect on the electrode array insertion pressure and the friction when higher insertion speeds are used compared with an uncoated electrode array. Therefore, PLLA is a suitable material to be used as a coating for CI electrode arrays and can be considered for a potential drug delivery system.

A novel method to efficiently isolate medullary thymic epithelial cells from murine thymi based on UEA-1 MicroBeads.

OBJECTIVE: The central mechanism for establishing a self-tolerant and functional T cell repertoire includes the promiscuous expression of otherwise tissue-restricted proteins by medullary thymic epithelial cells (TEC). We here demonstrate a novel and highly efficient method for isolating this rare key cell type. METHODS: We combined the enrichment of medullary TEC via UEA-1 MicroBeads with the subsequent depletion of residual CD45+ hematopoietic cells via specific size exclusion and compared our results to the standard Percoll enrichment method and isolation procedure via flow cytometric cell sorting. RESULTS: The addition of 2 µl UEA-1 MicroBeads per 108 thymus cells turned out best for optimal enrichment (an average of 22% purity compared to 1.2% for Percoll) and yield (an average of 1.73 × 105 medullary TEC per thymus compared to 5.16 × 104 for Percoll). After depletion of residual CD45+ cells, our method not only reached a purity of 75.5% but also turned out less stressful for the cells as compared to flow cytometric cell sorting. CONCLUSION: We here provide a fast and versatile procedure for enriching medullary TEC that yields higher purity and recovery rates than the standard Percoll enrichment method Our enrichment procedure in combination with CD45+ depletion via specific size exclusion is comparable to the current gold standard flow cytometric cell sorting method. SIGNIFICANCE STATEMENT: We developed a fast and versatile procedure to isolate a high number medullary TEC to investigate the biochemical processes of medullary TEC in more depths.

Circulating Soluble IL-6R but Not ADAM17 Activation Drives Mononuclear Cell Migration in Tissue Inflammation.

Neutrophil and mononuclear cell infiltration during inflammatory processes is highly regulated. The first cells at the site of infection or inflammation are neutrophils, followed by mononuclear cells. IL-6 plays an important role during inflammatory states. It has been shown in several models that the soluble form of IL-6R (sIL-6R) is involved in the recruitment of mononuclear cells by a mechanism called IL-6 trans-signaling. It had been speculated that sIL-6R was generated at the site of inflammation by shedding from neutrophils via activation of the metalloprotease ADAM17. Attempts to genetically delete the floxed ADAM17 gene selectively in myeloid cells infiltrating an air pouch cavity upon injection of carrageenan failed because in transgenic mice, LysMcre did not lead to appreciable loss of the ADAM17 protein in these cells. We therefore used ADAM17 hypomorphic mice, which only express ∼5% of ADAM17 wild-type levels in all tissues and show virtually no shedding of all tested ADAM17 substrates, to clarify the role of ADAM17 during local inflammation in the murine air pouch model. In the present study, we demonstrate that although IL-6 and the trans-signaling mechanism is mandatory for cellular infiltration in this model, it is not ADAM17-mediated shedding of IL-6R within the pouch that orchestrates this inflammatory process. Instead, we demonstrate that sIL-6R is infiltrating from the circulation in an ADAM17-independent process. Our data suggest that this infiltrating sIL-6R, which is needed for IL-6 trans-signaling, is involved in the controlled resolution of an acute inflammatory episode.