Aldosterone and prednisolone control of cochlear function in MRL/MpJ-Fas(lpr) autoimmune mice.

Recently this laboratory showed aldosterone, a mineralocorticoid that only enhances sodium transport, was as effective as the glucocorticoid prednisolone in restoring cochlear function in autoimmune mice. To further test this relationship between sodium transport and autoimmune hearing loss, dosage comparisons were made of prednisolone and aldosterone control of the auditory dysfunction in autoimmune MRL/MpJ-Fas(lpr) mice. Mice were tested at 2 months of age to establish baseline auditory brainstem response (ABR) thresholds, hematocrit, serum immune complexes, and anti-nuclear antibodies. Mice were then given different doses of prednisolone or aldosterone in their drinking water for 2 months. After the treatment period, most untreated water controls showed elevation of ABR thresholds due to the ongoing autoimmune disease. However, the steroid groups had significantly more mice with improved or unchanged thresholds. Both steroids improved stria vascularis morphology, although aldosterone appeared to be more effective. The immune suppressive prednisolone caused a dose-related improvement in levels of serum immune complexes and hematocrit, hallmarks of systemic autoimmune disease. Aldosterone, which has no immune suppressive function, did not alter systemic disease. The comparable efficacy of prednisolone and aldosterone in restoring auditory function suggests steroid reversal of autoimmune hearing loss in mice is due to increasing stria vascularis sodium transport and not suppression of systemic autoimmune reactions.

Auditory function in the C3H/HeJ and C3H/HeSnJ mouse strains.

The C3H inbred mouse strain arose in 1920 and includes several substrains, such as the C3H/HeJ and C3H/HeSnJ variants. However, use of these C3H mice in hearing research has been limited because their auditory function has not been described. Therefore, the purpose of this study was to characterize auditory function in two C3H representative substrains. C3H/HeJ and C3H/HeSnJ mice were obtained from Jackson Laboratories for auditory brainstem response (ABR) testing at ages from 2 to 30 months. Animals were tested with tone bursts at frequencies of 4,8,16,24, and 32 kHz. These early responses were evaluated for age-related threshold shifts as an index of peripheral auditory function. Both strains show normal sensitivity up to 14 months of age. Thresholds for both strains were slightly elevated at most frequencies at 18 months. C3H/HeSnJ mice tested at 30 months demonstrated little hearing function due to extensive sensorineural degeneration. Thus, these C3H strains maintain excellent cochlear function past 1 year of age.

Decreased auditory function in the C3H/lpr autoimmune disease mouse.

To better understand autoimmune-related inner ear disease, cochlear structure and function were evaluated in the C3H/lpr autoimmune strain mouse, a model for systemic lupus erythematosus. C3H/lpr mice were examined at ages from 2 to 12 months along with age-matched C3H/HeJ controls. Autoimmune disease onset occurred at 3-4 months of age as serum immune complexes, antinuclear antibodies, and spleen weights were significantly elevated. Auditory brainstem response (ABR) audiometry showed normal auditory thresholds in C3H/lpr mice at 4 months of age, but elevated thresholds by 6 months, particularly in the high frequencies. Examination of the cochleas revealed no apparent loss of hair cells or spiral ganglion neurons, even in those mice with 50 dB SPL threshold shifts. However, changes were observed in the stria vascularis, including edematous spaces, enlarged capillaries, and thickened vessel linings. These findings imply that cochlear dysfunction in the autoimmune disease mice is the result of stria vascularis pathology.

Rapid acquisition of auditory brainstem responses with multiple frequency and intensity tone-bursts.

Auditory brainstem response (ABR) thresholds, latency and amplitude functions were obtained in mice using stimuli presented singly and as a multiple stimulus sequence. All stimuli were tone-bursts at frequencies from 4 to 32 kHz. The multiple stimulus consisted of a sequence of 20 tone-bursts of four different frequencies at five intensities separated by 12 ms. A comparison of responses to stimuli presented singly and those obtained with the 20-stimulus train showed no significant difference in thresholds. Also, no differences were found in response latencies or amplitudes, indicating that the responses from multiple stimuli were not adapted or otherwise affected. The use of this 20-stimulus train can result in a significant time savings for data acquisition compared with single stimuli. These findings demonstrate the feasibility of the rapid acquisition of unadapted cochlear and brainstem responses at different frequencies using a sequence of tone-bursts at different frequencies and intensities.

Inner ear DNA receptors in MRL/lpr autoimmune mice: potential 30 and 70 kDa link between autoimmune disease and hearing loss.

Inner ear function and systemic autoimmune disease were evaluated in the MRL/lpr mouse to determine their relationship with alterations in cell surface DNA receptors of 28-30 and 68-70 kDa size. Auditory brainstem response thresholds in the autoimmune disease mice were significantly elevated as early as 2 months of age when compared to MRL/++ controls. Hearing thresholds continued to rise with progression of the disease, manifested as increasing spleen weights, antinuclear (anti-DNA) antibodies, and serum immune complexes. Cochlear membranous labyrinth cells in the autoimmune mice bound less DNA, suggesting the DNA receptors were abnormally occupied by circulating antibodies. Western blots of a murine T-cell line probed with autoimmune mouse sera demonstrated reactivity to 28-30 and 68-70 kDa proteins after disease onset. It is hypothesized that cell surface DNA binding molecules could be masked or down-regulated by circulating antibodies in autoimmune disease. This interference with DNA receptor activity may be occurring within the inner ear and underlie the cochlear dysfunction seen in autoimmune sensorineural hearing loss.

Failure of elevated heat shock protein 70 antibodies to alter cochlear function in mice.

Heat shock protein 70 (HSP70) has been suggested as the putative cochlear antigen underlying a proposed autoimmune etiology in certain cases of Meniere's disease and idiopathic hearing loss. To determine if antibodies to this cellular protein are capable of altering cochlear function, BALB/c (N= 3) and CBA/J (N= 9) mice were inoculated with bovine HSP70 by intraperitoneal injections (10 microg in saline) every 10 days for 7 or 10 months, respectively. An equal number of control mice were injected with PBS according to the same schedule. ABR thresholds at 4, 8, 16, and 32 kHz in the HSP70-inoculated mice did not change over the 10 month period and were similar to saline controls. Furthermore, serum immune complexes and antinuclear antibodies did not increase over the inoculation period. ELISA analysis demonstrated the mice created antibodies to the foreign HSP70, but these apparently caused no abnormalities in the auditory or immune systems. It was concluded that foreign HSP70 is antigenic and inoculation with it will raise antibodies, but these antibodies were neither immunopathogenic nor cochleopathic. Therefore, these findings do not support current theories that elevated anti-HSP70 antibodies are the underlying cause of hearing loss in patients with such antibodies present.

Steroid treatment improves cochlear function in the MRL.MpJ-Fas(lpr) autoimmune mouse.

Corticosteroid therapy is used to reverse autoimmune sensorineural hearing loss, although little is known of the mechanism by which this occurs. This has been due to the lack of a suitable animal model with spontaneous hearing loss that is steroid responsive. The present study examined the effects of prednisolone treatment on auditory thresholds in the MRL.MpJ-Fas(lpr) autoimmune mouse to determine its suitability as such a model. Autoimmune mice at 3.5-4. 5 months of age were evaluated by pure-tone auditory brainstem response (ABR) to establish threshold elevations due to the disease. The steroid treatment group was then given prednisolone in their drinking water for 2.5 months, while untreated controls were given tap water. Significantly more steroid treated mice survived to the time of post-treatment ABR evaluation. Half of the steroid treated ears demonstrated either improvement or no change in cochlear function compared to only 25% in the untreated controls. Overall, cochlear thresholds in the untreated controls increased by 14.7 dB, whereas no significant threshold increase was seen in the steroid treated group (4.3 dB) over the treatment period. No qualitative anatomical differences were seen in the ears of those mice surviving to the end of the study. These findings establish the autoimmune mouse as a model for studies of steroid responsive mechanisms within the ear. This could apply to autoimmune sensorineural hearing loss, as well as any hearing disorder for which steroid therapy is recommended.

Steroid treatment in young MRL.MpJ-Fas(lpr) autoimmune mice prevents cochlear dysfunction.

Corticosteroid therapy reverses clinical autoimmune sensorineural hearing loss, although little is known of how steroids restore normal auditory function. If suppression of systemic autoimmune processes underlies hearing restoration, then preventing autoimmune symptoms from developing should prevent cochlear dysfunction. MRL. MpJ-Fas(lpr) autoimmune mice were used to test this potential mechanism by initiating oral prednisolone treatment at 6 weeks of age, prior to autoimmune disease and hearing loss onset. The steroid treatment group was given prednisolone in their drinking water, while untreated controls were given tap water. Treatment continued for 7 months with periodic evaluations of cochlear function with auditory brainstem response (ABR) audiometry. Autoimmune mice given the steroid lived longer and did not develop levels of serum immune complexes seen in their untreated controls. Also, their ABR thresholds remained near normal throughout the 7 months of treatment, while untreated controls showed progressive threshold elevations typical for autoimmune disease. This correlation of suppressed systemic autoimmune activity and maintenance of normal cochlear function identifies one potential mechanism for autoimmune hearing loss and hearing restoration with steroid therapy. The autoimmune mouse should serve as a valuable model for future studies of the cochlear mechanisms responsive to steroid treatment in autoimmune hearing loss.

Aldosterone (mineralocorticoid) equivalent to prednisolone (glucocorticoid) in reversing hearing loss in MRL/MpJ-Fas1pr autoimmune mice.

HYPOTHESIS: Although the glucocorticoid prednisone is the standard therapy for autoimmune sensorineural hearing loss, what this hormone does in the ear to restore hearing is not known. MRL/MpJ-Fas(lPr) autoimmune mice consistently have shown only stria vascularis disease, implying that abnormal ion balances in the endolymph underlie cochlear dysfunction. Previously we have shown that hearing loss in these mice is reversed with prednisolone treatment. This, coupled with the complete lack of cochlear inflammation, suggests that the restoration of hearing with prednisolone is due to its sodium transport function and not to its anti-inflammatory or immune suppression effects. Therefore the hypothesis of this study was that the mineralocorticoid aldosterone, which only increases sodium transport, would be as effective as prednisolone in reversing autoimmune hearing loss. STUDY DESIGN: MRL/MpJ-Fas(lPr) autoimmune mice were treated with either prednisolone or aldosterone to compare steroid effects on auditory brainstem response (ABR) thresholds and stria morphology. METHODS: After baseline ABR audiometry, autoimmune mice were given prednisolone (5 mg/kg per day), aldosterone (15 microg/kg per day), or water in their drinking bottles. After 2 months of treatment the ABR thresholds were remeasured, and ears collected for histological examination. RESULTS: The untreated controls showed continued elevation of ABR thresholds and edematous stria. However, thresholds in most steroid mice were improved or unchanged and their stria morphology improved, particularly with aldosterone treatment. CONCLUSIONS: Restoration of hearing with steroid treatment is due to increased sodium transport to re-establish cochlear ionic balances. Aldosterone therapy may offer advantages over prednisone for long-term management of not only autoimmune hearing loss, but also other forms of nonimmune-related deafness for which steroids are currently prescribed.

Decreased cochlear DNA receptor staining in MRL.MpJ-Fas(lpr) autoimmune mice with hearing loss.

OBJECTIVES: Previous studies of decreased cochlear DNA binding in autoimmune mice suggested that antibodies against a cochlear cell surface DNA receptor cause autoimmune hearing loss. However, the presence of a cochlear DNA receptor has not been determined. Therefore, immunohistochemistry with an anti-DNA receptor antibody was performed on MRL.MpJ-Fas(lpr) (MRL/lpr) autoimmune mice to determine 1) which inner ear structures contain DNA receptors and 2) whether the receptor staining pattern changes as autoimmune disease progresses and hearing thresholds increase. STUDY DESIGN: A prospective study of the progression of hearing loss in autoimmune mice and correlated alterations in immunostaining for the inner ear DNA receptor. METHODS: One group of MRL/lpr mice (n = 10) was allowed to develop autoimmune disease, and auditory brainstem response (ABR) audiometry was performed at 4, 6, and 9 months of age to measure the progression of hearing loss. A second group (n = 5) was tested for ABR thresholds at 2 months of age and immediately killed to assess receptor staining before the onset of autoimmune disease and hearing loss. The inner ears from all mice were immunohistochemically stained with an anti-DNA receptor antibody, and a qualitative analysis of the staining of cochlear structures was performed. RESULTS: Auditory brainstem response audiometry revealed a significant 20- to 30-dB elevation of thresholds as systemic disease progressed. Anti-DNA receptor staining was heaviest in the spiral ligament and less intense in the spiral ganglion and cochlear nerve. Both groups showed a similar pattern of staining in these structures. The stria vascularis and hair cells also stained in both groups. However, the stria cells of normal-hearing mice showed diffuse intracellular immunoreactivity, whereas older mice displayed less staining that was confined to the cell membranes. CONCLUSIONS: The inner ears of MRL/lpr mice contain DNA receptors. Autoimmune hearing loss was correlated with weaker overall intracellular staining in the stria vascularis and hair cells but increased staining of the cell membranes. This suggested DNA receptors have impaired endocytosis and more receptors remain on the cell membrane, possibly as a result of binding by circulating autoantibodies.

Normal cochlear function in mdx and mdx(Cv3) Duchenne muscular dystrophy mouse models.

OBJECTIVES/HYPOTHESIS: Sensorineural hearing loss has been found in association with inherited muscular dystrophies in humans and in mouse models. An increased brainstem auditory evoked response threshold has been previously reported in the dystrophin-deficient mdx mouse model for Duchenne muscular dystrophy, suggesting that full-length dystrophin (Dp427) is involved in hearing. The objective of the present study was to confirm cochlear dysfunction with this gene defect and determine whether the shorter carboxyl terminus isoforms of dystrophin are also critical in maintaining normal hearing. STUDY DESIGN: Case controlled. Animal model. METHODS: Auditory brainstem response (ABR) audiometry to pure tones was used to evaluate cochlear function. Fourteen mdx, 4 mdx(Cv3), and 13 age-matched control (C57BL/6J and C57BL/10ScSn) male mice were tested at 5 weeks and 11 weeks of age. The ABR thresholds to tone-burst stimuli at 4, 8, 16, and 32 kHz were obtained for each ear and statistically compared (ANOVA) for potential group differences. RESULTS: Both mdx and mdx(Cv3) mice demonstrated normal ABR thresholds when compared with controls. CONCLUSIONS: Both mdx and mdx(Cv3) mouse models have normal hearing by ABR. The authors' data suggest that dystrophin and its carboxyl terminus isoforms do not play a critical role in hearing in the mouse. This was unexpected, as previous studies using the brainstem auditory evoked response method suggested that the mdx mouse has an increased threshold for hearing.

Quantitative relationships of the interaction between sound and kanamycin.

It is well known that the ototoxicity resulting from the use of aminoglycoside antibiotics in experimental animals can be augmented by intense sound. However, the dose-effect relationship of this interaction is not known. This study was designed to determine the shape of this dose-effect relationship in guinea pigs at sound intensities approaching those that would be experienced by patients receiving aminoglycoside antibiotics. We found a linear relationship between the probit of the percent of missing cochlear outer hair cells and decibel-A scale sound intensity when the animals were treated with kanamycin plus white noise ranging from 115 to 45 dBA.

Augmented gentamicin ototoxicity induced by vancomycin in guinea pigs.

Vancomycin has been reported to be an ototoxic drug in the clinical literature. At best, this literature is confusing. There are no reports of ototoxicity of vancomycin in experimental animals, even when it is administered concurrently with ethacrynic acid, a drug known to augment the ototoxic effect of most other ototoxic drugs. In most of the cases of permanent ototoxicity that have been reported, the patient was treated with an aminoglycoside antibiotic as well as vancomycin. This study found no evidence of vancomycin ototoxicity in guinea pigs, but found that vancomycin greatly enhanced the ototoxicity of gentamicin.

Steroid-responsive cochlear dysfunction in the MRL/lpr autoimmune mouse.

Corticosteroids historically have been used to treat autoimmune sensorineural hearing loss, although little is known of how steroids restore normal inner ear function. Therefore, to identify a potential model for this field of research, this study examined the effects of prednisolone on auditory brain stem response thresholds in the MRL/lpr mouse model of autoimmune sensorineural hearing loss. Mice treated with prednisolone after auditory threshold elevations demonstrated significant improvement and stabilization of thresholds compared with untreated controls. MRL/lpr mice treated with steroids before the onset of autoimmune disease and cochlear dysfunction demonstrated decreased serum immune complexes, higher survival rates, and lower auditory thresholds compared with untreated controls. These positive results suggest the autoimmune mouse may be useful for studies of steroid-responsive mechanisms of the cochlea in autoimmune sensorineural hearing loss, as well as any hearing disorder in which steroid therapy is currently used.

Otitis media incidence and impact on the auditory brain stem response in lipopolysaccharide-nonresponsive C3H/HeJ mice.

Although mice of the C3H strain normally respond to bacterial lipopolysaccharide with appropriate immune system activation, mice of the C3H/HeJ substrain do not because of a gene defect. This suggests they may be more susceptible to opportunistic bacterial infections and more likely to have otitis media than a normally responding substrain, such as the C3H/HeSnJ. Therefore these two substrains were evaluated for incidence of spontaneous middle ear disease at 2, 4, 6, 10, 12, 15, and 18 months of age. Auditory brain stem response audiometry to pure tones of 4, 8, 16, 24, and 32 kHz was performed to establish the impact of middle ear disease on auditory function. None of the lipopolysaccharide-responsive C3H/HeSnJ mice demonstrated middle ear disease. However, middle ear disease was present in 33% of the C3H/HeJ mice. The conductive loss caused by the otitis media resulted in auditory brain stem response threshold shifts of 15 to 40 dB SPL, lowered peak amplitudes, and increased latencies. Reduced lipopolysaccharide responsiveness by C3H/HeJ mice makes them less capable of reacting immunologically to bacterial infection and presumably underlies the failure to clear middle ear disease. The C3H/HeJ mouse may provide a valuable model in which to study lipopolysaccharide biologic activity and related middle ear inflammatory or immune mechanisms.

Twenty-stimulus train for rapid acquisition of auditory brainstem responses in humans.

This study addressed the clinical need to obtain frequency-specific auditory brainstem responses (ABRs) more rapidly than is currently possible. ABRs were obtained from 20 subjects using two different methods: a conventional method with tone bursts presented singly and a multiple-stimulus method using a train of 20 tone bursts. For both methods, tone bursts were presented at frequencies 1, 2, 4, and 8 kHz, shaped with a Blackman-Harris window and having intensity levels up to 105 dB peak equivalent sound pressure level (peSPL). The single tone bursts were presented at a 17.2/sec repetition rate. The 20 tone-burst train used the four frequencies at five intensities each and a repetition rate of 3.7/sec (separations between tone bursts of 9-12 msec, with 77 msec off-time between trains). Mean latencies and mean amplitudes for wave V were compared using t-tests for each of 12 conditions (four frequencies, each at the three highest output levels). For latency, only one comparison was significantly different (2 kHz, 77 dB peSPL). Similarly, only one comparison was significant for amplitude (2 kHz, 97 dB peSPL). There was, however, a trend for the tone bursts presented in trains to have longer latencies and reduced amplitudes compared to the respective responses for the single tone-burst condition. These results indicate the presence of some response adaptation when tone bursts are presented in a train. The use of a properly designed stimulus train can result in a significant time savings for obtaining frequency-specific ABRs as compared with single tone-burst presentations.

Fungal tunneling of hair from a buried body.

Tunnels produced in human head hair by fungal hyphae were examined with a light microscope and with a scanning electron microscope. The tunnels had small diameters and exhibited minimal branching. The use of a backscattered electron detector facilitated the locating of the openings of the tunnels in the surfaces of the hairs. In the backscattered electron image, tunnel openings appeared as dark spots. The tunneling hyphae did not show a preference for a particular location for entering the shaft of the hair. Some hyphae penetrated under the free edges of the cuticular scales, while others burrowed through the surfaces of the scales.

Comparison of fingernail striation patterns in identical twins.

The fingernail ridge patterns of a pair of identical twins were compared to each other, their parents, and an unrelated subject. The patterns of the twins' nails showed regions of strong similarity but were distinguishable from one another. Fewer similarities were found when comparing the nails to those of the parents and the unrelated control. The twins were shown to be monozygotic by means of DNA profiling. This therefore represents the first demonstration of unique fingernail ridge patterns in subjects shown conclusively to be identical twins. When the fingernail ridge patterns were examined with a scanning electron microscope, the backscattered electron (BEI) images were found to have superior contrast when compared to the secondary electron (SEI) images.

Mechanism of Agrobacterium beta-glucosidase: kinetic studies.

The beta-glucosidase from Agrobacterium faecalis (previously Alcaligenes faecalis) has been subjected to a detailed kinetic investigation with a range of substrates to probe its specificity and mechanism. It has a relatively broad specificity for the substrate sugar moiety and exhibits a classical pH dependence for its kinetic parameters with three different substrates and an identical pH dependence for its inactivation by a mechanism-based inactivator, cyclophellitol. Measurement of kcat and Km values for a series of aryl glucoside substrates has allowed construction of a Bronsted plot, the concave-downward shape of which is consistent with the anticipated two-step mechanism involving a glucosyl-enzyme intermediate which is formed and hydrolyzed via oxocarbonium ion-like transition states. The slope of the leaving group-dependent portion of the Bronsted plot (beta 1g = -0.7) indicates a large degree of bond cleavage at the transition state. Secondary deuterium kinetic isotope effects measured for five different aryl glucosides are also consistent with this mechanism and further suggest that the transition state for formation of the glucosyl-enzyme intermediate, probed with the slower substrates for which kH/kD = 1.06, is more SN2-like than that for its hydrolysis (for which kH/kD = 1.11). Reasons for this difference are proposed, and values of Ki for several ground-state and transition-state analogue inhibitors are presented which support the concept of sp2-hybridized transition states.

Inactivation of a beta-glucosidase through the accumulation of a stable 2-deoxy-2-fluoro-alpha-D-glucopyranosyl-enzyme intermediate: a detailed investigation.

The inactivation of glycosidases by 2-deoxy-2-fluoroglycosides has been shown previously to occur via the accumulation of a covalent 2-deoxy-2-fluoro-alpha-D-glucopyranosyl enzyme intermediate [Withers, S. G., & Street, I. P. (1988) J. Am. Chem. Soc. 110, 8551]. Further characterization of this process with Agrobacterium beta-glucosidase is described, and the range of glycosides engaging in this behavior is examined. Inactivation is shown to be accompanied by the release of a stoichiometric "burst" of aglycon, thereby providing a new class of active site titration agents for glycosidases. The rate of inactivation is shown to be very strongly dependent on the leaving group ability of the aglycon, the slowest inactivator studied (p-nitrophenyl2-deoxy-2-fluoro-beta-D-glucopyranoside) yielding only partial inactivation due to turnover of the intermediate becoming competitive with its formation. Such turnover of the intermediate is shown to be greatly accelerated by transglycosylation to a suitable glycoside bound in the aglycon site, resulting in the release of a disaccharide product which was isolated and characterized. The pH dependences of both the formation and the hydrolysis of the 2-deoxy-2-fluoroglycosyl-enzyme closely resemble those of each step for normal catalysis, indicating that the same catalytic groups are involved in both processes. A model system for the partial "steady-state" inactivation observed previously [Withers, S. G., Rupitz, K., & Street, I. P. (1988) J. Biol. Chem. 263, 7929] with certain other glycosidases was established by incubating the enzyme with an inactivator known to undergo relatively rapid transglycosylation in the presence of various concentrations of a suitable reactivator.(ABSTRACT TRUNCATED AT 250 WORDS)