Biomedical subjects

Elizabeth M Keithley

Publications and source records attributed to Elizabeth M Keithley.

16 recordsLinked to original sources

PubMed2006

Immune cell recruitment following acoustic trauma.

Acoustic trauma induces cochlear inflammation. We hypothesized that chemokines are involved in the recruitment of leukocytes as part of a wound healing response. The cochleas of NIH-Swiss mice, exposed to octave-band noise (8-16 kHz, at 118 dB) for 2h, were examined after the termination of exposure. Leukocytes were identified immunohistochemically with antibodies to CD45 and F4/80. Gene array analysis followed by RT-PCR was performed on cochlear tissue to identify up-regulation of chemokine and adhesion molecule mRNA. The expression of the adhesion molecule ICAM-1 was also investigated immunohistochemically. Few CD45- or F4/80-positive leukocytes were observed in the non-exposed cochlea. Following acoustic trauma however, the number of CD45-positive cells was dramatically increased especially after 2 and 4 days, after which time the numbers decreased. F4/80-positive cells also increased in number over the course of a week. Gene array analysis indicated increased expression of monocyte chemoattractant protein 5 (MCP-5), monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein-1beta (MIP-1beta) and ICAM-1. RT-PCR, performed using primers for the individual mRNA sequences, confirmed the increased expression of MCP-1, MCP-5, MIP-1beta, and ICAM-1 relative to non-exposed mice. In the normal cochlea, ICAM-1 immunohistochemical expression was observed in venules, spiral ligament fibrocytes and in endosteal cells of the scala tympani. Expression increased to include more of the spiral ligament and endosteal cells after acoustic trauma. A cochlear inflammatory response is initiated in response to acoustic trauma and involves the recruitment of circulating leukocytes to the inner ear.

Animals↗

PubMed2006

Effects of antioxidants on the aging inner ear.

Age-related cochlear structural changes include the degeneration of sensory, neural cells and the stria vascularis. The hypothesis that cellular degeneration results from exposure to oxidative products of respiration was tested by supplementing aged dogs with a diet high in antioxidants and mitochondrial metabolites and by genetically modifying the expression level of the antioxidant, manganese superoxide dismutase (SOD2) in mice. Aged dogs received either a high antioxidant diet or a normal, control diet for the last 3 years of their life. Cellular measures were compared among the two aged groups (10-15 years) and young dogs. Both aged groups had cellular degeneration relative to young dogs, but the animals fed the antioxidant diet showed less degeneration at the base and apex than the control-diet group. Transgenic mice, heterozygous null for SOD2, produce only half as much enzyme as a normal mouse. These mice showed no increase in the amount of hearing loss relative to the background strain. A diet containing antioxidants reduced the magnitude of cochlear degeneration. Genetic reduction of one antioxidant, however, did not increase the magnitude of hearing loss in aging mice. A reduction in one enzyme seems to be compensated while the addition of a complex of factors is effective.

Aging↗

PubMed2006

Transforming growth factor beta expression during an inner ear immune response.

OBJECTIVES: The involvement of transforming growth factor beta (TGF-beta), a strong mediator of fibrogenesis, during cochlear immune responses was investigated. METHODS: An inner ear adaptive immune response to antigen was created in mice that were painlessly sacrificed 3 to 48 hours and 7 days after initiation of the immune response. The cochleas were assayed by immunocytochemistry for TGF-beta and latency-associated peptide (LAP). RESULTS: We found LAP expressed in normal cochleas and the endolymphatic sac, in the small round cells in the cochlear scalae and the mesothelial cells under the basilar membrane, and in the endolymphatic sac perisaccular area. We found TGF-beta expressed in infiltrated, inflammatory cells in the scalae and the endolymphatic sac lumen 3 hours after cochlear antigen challenge. At this time, LAP immunoreactivity was decreased. This rapid shift in immunoreactivity provides evidence for activation of TGF-beta during an immune response. This reversal of expression persisted for 48 hours, but conditions reverted to normal after 7 days. Surgical controls did not show TGF-beta expression. CONCLUSIONS: We conclude that TGF-beta activation occurs in the early phase of a cochlear adaptive immune response and is down-regulated as the response resolves. This finding suggests that the process of cochlear fibrosis starts early and that proper treatment could prevent cochlear fibrosis.

Animals↗

PubMed2005

Cu/Zn superoxide dismutase and age-related hearing loss.

Mice, in which the genetics can be manipulated and the life span is relatively short, enable evaluation of the effects of specific gene expression on cochlear degeneration over time. Antioxidant enzymes such as Cu/Zn superoxide dismutase (SOD1) protect cells from toxic, reactive oxygen species and may be involved in age-related degeneration. The effects of SOD1 deletion and over-expression on the cochlea were examined in Sod1-null mice, Sod1 transgenic mice and in age- and genetics-matched controls. Auditory brainstem responses (ABR) were measured and cochleae were histologically examined. The absence of SOD1 resulted in hearing loss at an earlier age than in wildtype or heterozygous mice. The cochleae of the null mice had severe spiral ganglion cell degeneration at 7-9 months of age. The stria vascularis in the aged, null mice was thinner than in the heterozygous or wildtype mice. Over-expression of SOD1 did not protect against hearing loss except at 24 months of age. In conclusion, SOD1 seems important for survival of cochlear neurons and the stria vascularis, however even half the amount is sufficient and an over abundance does not provide much protection from age-related hearing loss.

Aging↗

PubMed2005

Eya1 acts upstream of Tbx1, Neurogenin 1, NeuroD and the neurotrophins BDNF and NT-3 during inner ear development.

Cell fate specification during inner ear development is dependent upon regional gene expression within the otic vesicle. One of the earliest cell fate determination steps in this system is the specification of neural precursors, and regulators of this process include the Atonal-related basic helix-loop-helix genes, Ngn1 and NeuroD and the T-box gene, Tbx1. In this study we demonstrate that Eya1 signaling is critical to the normal expression patterns of Tbx1, Ngn1, and NeuroD in the developing mouse otocyst. We discuss a potential mechanism for the absence of neural precursors in the Eya1-/- inner ears and the primary and secondary mechanisms for the loss of cochleovestibular ganglion cells in the Eya1bor/bor hypomorphic mutant.

Animals↗

PubMed2005

Cochlear microperfusion: experimental evaluation of a potential new therapy for severe hearing loss caused by inflammation.

HYPOTHESIS: Cochlear microperfusion will be a useful treatment of severe sensorineural hearing loss caused by inflammation. BACKGROUND: Viruses, bacteria, and autoimmunity can initiate inflammation in the inner ear. The acute phase is associated with elevations in cytokines, nitrous oxide, and cellular infiltrates and the breakdown of the blood-labyrinthine barrier. The chronic phase leads to irreversible ossification of the labyrinth. METHODS: The authors developed cochlear microperfusion to facilitate removal of inflammatory cells and their byproducts during the acute phase of inflammation. Using a ventral approach to the guinea pig cochlea, the authors displaced resident perilymph by delivering perfusate into the scala vestibuli and collecting the effluent from the scala tympani. The authors evaluated the benefit of the procedure in an animal model of severe hearing loss caused by inflammation. RESULTS: Healthy controls undergoing cochlear microperfusion with phosphate-buffered saline incurred a mean hearing loss of 16 dB (n=4). This hearing loss was associated with the creation of two cochleostomies and not the perfusion itself. Sterile labyrinthitis (n=5) generated by perfusion of the cochlea with antigen consistently produced severe hearing loss over the initial 48 hours, and this hearing loss persisted for the subsequent 7 days. Therapeutic cochlear microperfusion, performed within the first 24 hours of developing severe hearing loss (n=9), immediately restored on average 24 dB (p <0.007) of hearing. CONCLUSION: Cochlear microperfusion is a promising new technique for treating severe deafness caused by inflammation. The benefit may be sustained when combined with local delivery of immunosuppressive agents to the inner ear.

Animals↗

PubMed2004

Innate immunity contributes to cochlear adaptive immune responses.

Inner ear immune responses mediated by antigen-specific processes are thought to contribute to hearing loss in humans. Systemic activation of innate immunity contributes to immune responses in the central nervous system. We hypothesized that activation of innate immunity can prime the inner ear for adaptive immune responses and exacerbate disease. Mice were systemically immunized with antigen. Three weeks after initial antigen exposure, the antigen was injected intrathecally coincident with systemic injection of lipopolysaccharide (LPS), an activator of innate immunity. Responses were measured by quantifying the leukocyte infiltrate and cochlear IL-1beta expression. LPS stimulation markedly amplified the adaptive immune response to exogenous antigen in the inner ear. These data indicate that the cochlea is activated by systemic events that stimulate innate immunity and when antigen is present in the inner ear, a robust cochlear adaptive response is generated. If true in humans, this implies that priming may be an important component in the development of immune-mediated hearing loss.

Adjuvants, Immunologic↗

PubMed2004

Age-related hearing loss and the ahl locus in mice.

C57BL/6 (B6) mice experience hearing loss and cochlear degeneration beginning about mid-life, whereas CAST/Ei (CAST) mice retain normal hearing until old age. A locus contributing to the hearing loss of B6 mice, named age-related hearing loss (ahl), was mapped to Chromosome 10. A homozygous, congenic strain of mice (B6.CAST-+ahl ), generated by crossing B6 (ahl/ahl) and CAST (+ahl/+ahl) mice has the same genomic material as the B6 mice except in the region of the ahl locus, which is derived from CAST. In this study, we have determined the extent of the CAST-derived region of Chromosome 10 in the congenic strain and have examined mice of all three strains for hearing loss and cochlear morphology between 9 and 25 months of age. Results for B6 mice were similar to those described previously. CAST mice showed no detectable hearing loss even at 24 months of age; however, they had a small amount of ganglion cell degeneration. B6.CAST-+ahl mice were protected from early onset hearing loss and basal turn degeneration, but older animals did show some hearing loss and ganglion cell degeneration. We conclude that loci in addition to ahl contribute to the differences in hearing loss between B6 and CAST mice. These results illustrate the complex inheritance of age-related hearing loss in mice and may have implications for the study of human presbycusis.

Aging↗

PubMed2003

Proinflammatory cytokine expression in the endolymphatic sac during inner ear inflammation.

The inner ear is capable of rapidly mounting an immune response that can ultimately lead to cochlear degeneration and permanent hearing loss. The role of the endolymphatic sac in this immune process is not clear. In order to investigate the cytokine expression of cells within the endolymphatic sac, a secondary inner ear immune response to keyhole limpet hemocyanin (KLH) was created in mice. The animals were sacrificed 3-48 h and 7 days following initiation of the immune response. The cochleas and endolymphatic sacs were assayed by immunocytochemistry for IL-1beta, TNFalpha, and IL-6. Three hours after KLH challenge of the scala tympani, the perisaccular tissue of the endolymphatic sac contained more inflammatory cells than the scala tympani or endolymphatic sac lumen. Only a few of these cells, however, expressed the proinflammatory cytokines IL-1beta and TNFalpha between 3 and 12 h after KLH injection. On the other hand, TNFalpha, which plays an important role in the cochlear secondary immune response, was expressed in cells in the endolymphatic sac lumen. The maximum percentage of cells expressing TNFalpha was seen later than in the scala tympani. Animals treated with systemic injection of the TNF blocker, etanercept, showed a reduction in the number of cells in the endolymphatic sac lumen. It is concluded that the cells in the endolymphatic sac lumen contribute to the amplification of the adaptive immune response by expressing TNFalpha, while the infiltration of cells into the perisaccular connective tissue is part of the nonspecific, innate, cochlear immune response.

Animals↗

PubMed2003

Blockage of immune-mediated inner ear damage by etanercept.

HYPOTHESIS: Etanercept will be able to reduce the inflammation and hearing loss associated with experimentally induced labyrinthitis. BACKGROUND: Inner ear immune responses cause hearing loss that may be reversible with pharmacologic treatment. Etanercept, tumor necrosis factor receptor blocker, was investigated in a guinea pig model of immune-mediated hearing loss. Sterile labyrinthitis was created by injection of keyhole limpet hemocyanin into the inner ear after systemic sensitization to keyhole limpet hemocyanin with adjuvant. Labyrinthitis involves infiltration of inflammatory cells and hearing loss detectable 3 to 5 days after challenge with keyhole limpet hemocyanin. METHODS: Etanercept was administered either systemically (2.5 mg) 30 minutes before intracochlear challenge with keyhole limpet hemocyanin, with a second intraperitoneal dose (2.5 mg) 3 days later or locally by long-term infusion into the scala tympani with an osmotic pump (5.0 microg/h for 7 days). Auditory evoked brainstem response thresholds were measured before and after treatment to determine hearing loss. Cochleas were evaluated for the amount of inflammation. RESULTS: Hearing loss in the untreated systemic group averaged 71 +/- 21 dB versus 37 +/- 32 dB in the etanercept-treated animals (t test, P < 0.001). There was also less inflammation in the cochleas from etanercept-treated animals (t test, P < 0.01). Hearing loss with local administration of etanercept was 59 +/- 31 dB in the nontreated ears and 18 +/- 8 dB in the treated ears (t test, P < 0.02). Inflammation was also less (t test, P < 0.01). Etanercept was not ototoxic. CONCLUSION: Prompt intervention with the anti-inflammatory drug etanercept significantly reduces inflammation sufficient for substantive hearing preservation.

Animals↗

PubMed2002

Inflammatory signals increase Fas ligand expression by inner ear cells.

There is considerable evidence that hearing and vestibular function can be influenced by immune processes. The inner ear has evolved mechanisms, such as the blood-labyrinthine barrier that limit immune responses and autoimmune processes to reduce the potential for damage to cochlear cells. Recently, expression of Fas ligand (FasL) in some non-lymphoid tissue, as in the anterior chamber of the eye, has been hypothesized to play a role in protection of sensitive organs from activated T-cells. We show that under resting conditions, cochlear cells express little or no FasL. However, after exposure to interferon-gamma in vitro, FasL is induced in many neonatal cochlear cells. In addition, we show that FasL is upregulated in adult cochlear cells after induction of a sterile labyrinthitis in vivo. The induction of FasL by inflammation may serve to limit cochlear immune responses, and to protect sensorineural tissue from immune and autoimmune damage.

Animals↗

PubMed2002

Immune-mediated hearing loss: basic mechanisms and options for therapy.

Immune responses are an important component of the defense of the inner ear against infection. However, immunity appears to be restricted in the labyrinth, as the inflammation associated with immune responses can damage the delicate cellular structures that mediate hearing and balance. When immunoregulation is compromised, either experimentally or through disease, immune-mediated inner ear damage and hearing loss can result. Because there are few resident leukocytes within the labyrinth, immunity and inflammation are mediated primarily by cells that enter the inner ear following the activation of post-capillary venules, which in the cochlea are the spiral modiolar veins. Activated lymphocytes are an important component of the infiltrating leukocytes, and their interactions with antigen mediate inner ear immunity. While evidence of autoimmunity specific to the inner ear is incomplete, an autoimmune origin is often suspected in idiopathic, bilateral, rapidly progressive hearing loss. Systemic immunosuppressive drugs can be effective in reversing such hearing loss, although at the cost of occasionally severe side-effects. Experimental evidence suggests that local therapy may be effective in treating this condition, if it were to target the infiltration of leukocytes into the labyrinth.

Animals↗

PubMed2002

Tumor necrosis factor-alpha, an initiator, and etanercept, an inhibitor of cochlear inflammation.

OBJECTIVES/HYPOTHESIS: The inner ear rapidly mounts an immune response that can lead to cochlear degeneration and permanent hearing loss. Identification of proinflammatory cytokine expression during the initiation of the response should lead to rational therapeutic strategies that block the response, reducing damaging sequelae. STUDY DESIGN: A cochlear immune response to keyhole limpet hemocyanin (KLH) injected into the inner ear or subarachnoid space of sensitized animals was created. Etanercept was administered to a group of animals to blunt the immune response. METHODS: Cochleae were immunoassayed for expression of interleukin-1beta, tumor necrosis factor-alpha, and interleukin-6 and evaluated for the amount of cochlear-infiltrated cells. RESULTS: Tumor necrosis factor-alpha and interleukin-1beta were expressed by infiltrated cells shortly after KLH injection. Tumor necrosis factor-alpha was expressed whether the antigen was introduced with or without surgical trauma. Interleukin-1beta was also expressed by the cochlear fibrocytes during the immune response and in surgical control animals, but not after intrathecal injection of antigen. Interleukin-6 expression was minimal during the response. Based on this observation, animals were treated with systemic injection of Etanercept, which reduced cochlear infiltrating cell number and cochlear fibrosis. CONCLUSION: Interleukin-1beta expression is a general cochlear response to trauma, whereas tumor necrosis factor-alpha expression in the infiltrated immunocompetent cells is the cytokine that induces amplification of the response that leads to cochlear disease.

Animals↗

PubMed2002

Immunological damage to the inner ear: current and future therapeutic strategies.

There is considerable evidence to suggest that hearing and vestibular function can be influenced by immunity in the inner ear. While immunity can protect against infections of the labyrinth, immune response also has the capacity to damage the delicate tissues of the inner ear. Antigenic challenge of the inner ear of sensitized animals leads to rapid accumulation of leukocytes, antibody production, hearing loss and tissue damage. Moreover, a number of systemic autoimmune disorders include hearing loss and vertigo as part of their constellation of symptoms. It also appears that autoimmune damage can exist as an entity confined to the labyrinth. Immune disorders of the inner ear are of special interest since they are among the few forms of hearing loss that are currently amenable to medical treatment. In addition, recent developments in understanding the intracellular pathways that participate in damage to the inner ear provide new opportunities for pharmacotherapy of immune-mediated disorders of hearing and balance.

Animals↗

PubMedDate not supplied

A case against spiral ligament atrophy as a cause of Ménière's disease.

The etiology of Ménière's disease and endolymphatic hydrops has been very difficult to determine. In order to develop rational therapies for patients with Ménière's disease the etiology needs to be established. In the current study an examination was made of the spiral ligament in temporal bones from individuals with Ménière's and endolymphatic hydrops and normal control temporal bones. No evidence of atrophy in either the length or width or the fibrocyte cell density was seen in the temporal bones with Ménière's disease. The role of the spiral ligament in the development of endolymphatic hydrops is still unclear.

Animals↗

PubMedDate not supplied

Induction of MHC class II antigens on cells of the inner ear.

Growing evidence supports the concept that immune reactions occur in the cochlea, where they can function either in protection or as a source of inflammation. Since immunity is generally initiated by antigen presentation of foreign substances to T cells, antigen-presenting cells expressing major histocompatibility complex (MHC) class II molecules are required. Under resting conditions, cochlear cells usually express no MHC class II. However, we show that exposure to -interferon in vitro induces an increase in MHC class II expression in neonatal cochlear cells of mice. In addition, MHC class II immunoreactivity was observed in the inner ear of adult mice after induction of sterile labyrinthitis in vivo. It is concluded that the induction of MHC class II molecules by inflammation may render cochlear cells competent to initiate and participate in immune reactions and may therefore contribute to both immunoprotective and immunopathological responses of the inner ear.

Animals↗