Effects of hydroxyethyl starch, nimodipine, and propylene glycol on cochlear blood flow

Repurposable Drugs That Interact with Steroid Responsive Gene Targets for Inner Ear Disease

Corticosteroids, oral or transtympanic, remain the mainstay for inner ear diseases characterized by hearing fluctuation or sudden changes in hearing, including sudden sensorineural hearing loss (SSNHL), Meniere's disease (MD), and autoimmune inner ear disease (AIED). Despite their use across these diseases, the rate of complete recovery remains low, and results across the literature demonstrates significant heterogeneity with respect to the effect of corticosteroids, suggesting a need to identify more efficacious treatment options. Previously, our group has cross-referenced steroid-responsive genes in the cochlea with published single-cell and single-nucleus transcriptome datasets to demonstrate that steroid-responsive differentially regulated genes are expressed in spiral ganglion neurons (SGN) and stria vascularis (SV) cell types. These differentially regulated genes represent potential druggable gene targets. We utilized multiple gene target databases (DrugBank, Pharos, and LINCS) to identify orally administered, FDA approved medications that potentially target these genes. We identified 42 candidate drugs that have been shown to interact with these genes, with an emphasis on safety profile, and tolerability. This study utilizes multiple databases to identify drugs that can target a number of druggable genes in otologic disorders that are commonly treated with steroids, providing a basis for establishing novel repurposing treatment trials.

Nimodipine and Steroid Combination Therapy for Idiopathic Sudden Sensorineural Hearing Loss

OBJECTIVE

To evaluate the treatment outcomes of nimodipine and steroid combination therapy for idiopathic sudden sensorineural hearing loss (ISSNHL).

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

Seventy-eight patients who were diagnosed with ISSNHL were divided into two group based on the treatment strategies used: steroid+nimodipine (SN, n = 36) and steroid only (SO, n = 42) groups. Based on the level of hearing loss before treatment, subgroup analysis (<90 dB HL, SN-S versus SO-S groups; ≥90 dB HL, SN-P versus SO-P groups) was performed.

INTERVENTIONS

Nimodipine+dexamethasone versus dexamethasone alone.

MAIN OUTCOME MEASURES

Hearing thresholds and complete/partial recovery rate after treatment.

RESULTS

Hearing thresholds after treatment were not significantly different between the SN and SO groups (46.8 ± 29.4 versus 54.8 ± 27.6 dB HL, p = 0.218). However, the complete recovery rate was significantly higher in the SN group than in the SO group (41.7% versus 16.8%, p = 0.014). In subgroup analysis, the complete recovery rate was significantly higher in the SN-S group than in the SO-S group (60.9% versus 19.2%, p = 0.003), whereas the difference between the SN-P and SO-P groups was not significant (7.7% versus 12.5%, p = 0.672). The cumulative incidence of complete recovery was significantly higher in SN-S group than in the SO-S group (p = 0.005); the mean recovery time was 4.4 weeks (95% confidence interval [CI], 2.8-6.1) in the SN-S group and 8.8 weeks (95% CI, 7.0-10.5) in the SO-S group.

CONCLUSIONS

The results of this study suggest that nimodipine and steroid combination therapy for ISSNHL results in a higher complete recovery rate than steroid alone in patients with moderate to severe hearing loss.

Idiopathic sudden sensorineural hearing loss in children

OBJECTIVE

Although idiopathic sudden sensorineural hearing loss (ISSHL) is a frequent disease in adults, less is known about incidence and treatment of ISSHL in children.

METHOD

A retrospective chart analysis was performed to evaluate the frequency of ISSHL in children aged under 18 years between 2000 and 2003, who were treated in our department. Children received prednisolone intravenously at an initial dose of 3mg/kg bodyweight. Prednisolone dose was reduced to half every second day. The medication was given for a maximum of 14 days or finished 2 days after the hearing normalized in pure-tone audiometry. The follow-up was continued between 3 and 14 months.

RESULTS

The complete recovery rate was 57%, and the partial recovery was 36%. Initial hearing loss of 50dB and more was predictive for poor outcome in children (p=0.028). Presence of tinnitus was without relevance for the outcome. The incidence of ISSHL in the local area of about 250,000 inhabitants was 1/10,000 in children.

CONCLUSION

ISSHL seems to be a less frequent disease in children than in adults. Severe initial hearing loss is coupled with poor outcome. Under treatment with prednisolone hearing improvement was found in 13 of 14 patients.

Effects of nimodipine on salicylate ototoxicity

The purpose of this study was to examine the effects of nimodipine on salicylate ototoxicity in guinea pigs. The compound action potential (CAP) was recorded at the round window, and the cochlear blood flow (CBF) was measured simultaneously from the lateral wall of the basal turn of the cochlea by laser Doppler flowmetry. After administration of salicylate (100 mg/kg), the CAP thresholds were significantly elevated, by 5 to 20 dB (p < .05), and the CBF was significantly decreased (p < .05). After administration of nimodipine (2 mg/kg), the CAP thresholds were unchanged, but the CBF had increased significantly (p < .05), while systemic blood pressure had decreased significantly (p < .05). Simultaneous administration of both salicylate (100 mg/kg) and nimodipine (2 mg/kg) resulted in significant elevation of the CAP thresholds (p < .05), while the CBF did not decrease. These results suggest that nimodipine prevents the decrease in CBF induced by salicylate, but that nimodipine does not prevent the deterioration in the CAP.

The effect of blood flow promoting drugs on cochlear blood flow, perilymphatic pO(2) and auditory function in the normal and noise-damaged hypoxic and ischemic guinea pig inner ear

The effect of blood flow promoting drugs, such as hydroxyethyl starch (HES) either of low or high molecular weight (HES 70, HES 200), pentoxifylline, ginkgo biloba, naftidrofuryl and betahistine, and various combinations of the drugs was studied in unexposed and noise-exposed (broad-band noise, bandwidth 1-12 kHz, 106 dB SPL, 30 min) guinea pigs. The results were compared without therapy and placebo (isotonic saline, NaCl). The cochlear blood flow (CoBF) and the partial pressure of oxygen in the perilymph (PL-pO(2)) were continuously and simultaneously recorded over a period of 210 min. In addition, cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs) and auditory brain stem responses (ABRs) were registered. Noise-induced hearing loss (NIHL) paralleled a decrease of PL-pO(2). Both were found to occur before evidence of reduced CoBF. PL-pO(2) and CoBF declined progressively post-exposure, while CMs, CAPs and ABRs showed no further deterioration or signs of recovery up to 180 min after cessation of noise. Treatment started 60 min post-exposure, respectively after 90 min, without manipulation in unexposed animals, and was then studied for a further 120 min. In unexposed animals, CoBF increased significantly during infusion of HES 70, HES 200, pentoxifylline and betahistine. NaCl, ginkgo biloba and naftidrofuryl did not alter CoBF. PL-pO(2) decreased significantly during infusion of all administered drugs and combinations, except for NaCl. CMs, CAPs and ABRs remained constant, with the exception of increased ABRs after infusion of HES 70 and HES 200. In noise-exposed animals, a sustained therapeutic effect on cochlear ischemia was achieved only by HES 200 and pentoxifylline. HES 70, betahistine and ginkgo biloba compensated cochlear ischemia only during infusion; however, 30-60 min after termination of therapy, no significant difference of values for CoBF was observed compared to the untreated noise-exposed groups. NaCl and naftidrofuryl showed no effect on CoBF. None of the applied drugs had a sustained compensatory effect on cochlear hypoxia. CMs, CAPs and ABRs improved significantly after HES 70, HES 200 and betahistine, resulting in partial recovery of CMs, and partial (betahistine) or even full (HES 70 and HES 200) recovery of CAPs and ABRs. In contrast, NaCl, pentoxifylline, ginkgo biloba and naftidrofuryl had no therapeutic effect on NIHL.

Ca2+-dependence and nifedipine-sensitivity of vascular tone and contractility in the isolated superfused spiral modiolar artery in vitro

The regulation of the vascular diameter of the spiral modiolar artery may play a major role in the regulation of cochlear blood flow and tissue oxygenation since the spiral modiolar artery provides the main blood supply to the cochlea. The goal of the present study was to determine whether vascular tone and contractility of the spiral modiolar artery depend on the presence of extracellular Ca2+ and involves nifedipine-sensitive Ca2+ channels. The spiral modiolar artery was isolated and superfused in vitro and the diameter was measured continuously by video microscopy. Isolated segments of the spiral modiolar artery had an outer diameter of 61 +/- 3 microm (n = 59) and displayed vasomotion characterized by 5-15 clearly distinguishable constrictions per min. Removal of Ca2+ from the superfusion medium caused a reversible relaxation and cessation of vasomotion and was used to determine the magnitude of basal vascular tone. The basal vascular tone consisted of a sustained reduction of the vascular diameter to 95.1 +/- 0.3% (n = 51) of the maximal diameter in Ca2+-free medium. Nifedipine reduced the basal vascular tone with an IC50 of (1.1 +/- 0.3) x 10(-9)) M although 22% of the basal vascular tone was insensitive to nifedipine. Elevation of the K+ concentration from 3.6 to 150 mM caused a transient vasoconstriction which was dependent on the presence of extracellular Ca2+. Nifedipine fully inhibited K+-induced vasoconstriction with an IC50 of (2.0 +/- 0.7) x 10(-9) M. Norepinephrine (10(-4) M) caused a transient vasoconstriction and an increase of vasomotion at branch points of the spiral modiolar artery. Norepinephrine-induced vasoconstriction was fully inhibited in the absence of Ca2+ and partially inhibited by 10(-7) M nifedipine. These observations suggest that the spiral modiolar artery contains voltage-dependent nifedipine-sensitive Ca2+ channels which are involved in the maintenance of basal vascular tone as well as in the mediation of K+- and norepinephrine-induced contractility. Further, the data suggest that cytosolic Ca2+ stores, if present in the spiral modiolar artery, are of limited capacity compared to other vessels.

Nimodipine at a dose that slows ABR latencies does not protect the ear against noise

We tested the hypothesis that nimodipine, a dihydropyridine reported to increase blood flow, block calcium and potassium channels, and reduce ischemic damage, would alleviate noise-induced hearing loss. Young C57B1/6J mice were exposed to wide-band noise (2 min, 120 dB SPL), with ABR thresholds (4-50 kHz) determined before noise exposure, and from 1 h to 2 weeks afterwards. One group (n = 7) received nimodipine (30 mg/kg/day) in daily peanut butter food supplements beginning 24 h before exposure; the other group (n = 6) received peanut butter alone. In the pretest nimodipine significantly increased the latency of Wave P1 of the ABR (mean difference: 0.16 ms; P < 0.02), showing that calcium blockade depressed sensorineural efficiency, but ABR thresholds were not affected. Noise exposure produced a severe threshold loss that partially recovered in the first week after exposure, and then suffered a slight but significant loss in the second week. These effects were seen equally in both groups: nimodipine did not reduce the severity of the immediate hearing loss following noise exposure, nor did it benefit recovery.

The effect of nimodipine on cochlear potentials and Na+/K(+)-ATPase activity in normal and hydropic cochleas of the albino guinea pig

In experimental endolymphatic hydrops (EEH) a decrease in the endocochlear potential (EP) has been reported and is thought to be due to decreased activity of the enzyme Na+/K(+)-ATPase in the stria vascularis. By stimulating Na+/K(+)-ATPase, the EP, and thereby cochlear function as a whole, might be restored. On the other hand, stimulation of stria vascularis Na+/K(+)-ATPase might result in excessive production of endolymph and thus produce or augment hydrops. In this study we have investigated the effect of intraperitoneally applied nimodipine on cochlear potentials and on Na+/K(+)-ATPase activity in the stria vascularis, both in normal cochleas (control) and in cochleas with EEH. Nimodipine is an L-type Ca(2+)-channel blocking agent with Na+/K(+)-ATPase stimulating properties at concentrations as low as 1.5 nM. The compound action potential (CAP), evoked by 2,4 and 8 kHz tone bursts was found to be depressed in the EEH ears with and without nimodipine treatment, and in the nimodipine treated control ears. Statistical analysis (ANOVA) showed that the effects of EEH and nimodipine on the CAP were additive. The negative summating potential (SP), measured extracochlearly at the apex, in response to 4 and 8 kHz tone bursts was significantly enhanced in the EEH ears. Nimodipine treatment did not affect the SP, neither in the control, nor in the EEH ears. Cytochemically, Na+/K(+)-ATPase activity appeared to be decreased in the oedematous stria vascularis of hydropic cochleas. No effect of nimodipine on Na+/K(+)-ATPase activity could be established ultracytochemically, neither in the controls nor in the EEH ears. In the lower turns of some of the nimodipine treated control cochleas a mild hydrops was seen during light-microscopic evaluation. Although it was not possible to prove a stimulatory effect of nimodipine on the enzyme Na+/K(+)-ATPase cytochemically, the finding of mild endolymphatic hydrops in nimodipine treated control ears suggests (a history of) increased endolymph production. This hydrops might be responsible for the depression of the CAP in the nimodipine treated ears.

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.