Medical Therapy of Hearing Impairment and Tinnitus with Chinese Medicine: An Overview

The current review gives a comprehensive overview of the recent development in Chinese medicine (CM) for treating several kinds of acquired nerve deafness and tinnitus, as well as links the traditional principle to well-established pharmacological mechanisms for future research. To date, about 24 herbal species and 40 related ingredients used in CM to treat hearing loss and tinnitus are reported for the treatment of endocochlear potential, endolymph growth, lowering toxic and provocative substance aggregation, inhibiting sensory cell death, and retaining sensory transfer. However, there are a few herbal species that can be used for medicinal purposes. Nevertheless, clinical studies have been hampered by a limited population sample, a deficiency of a suitable control research group, or contradictory results. Enhanced cochlear blood flow, antiinflammatory antioxidant, neuroprotective effects, and anti-apoptotic, as well as multi-target approach on different auditory sections of the inner ear, are all possible benefits of CM medications. There are numerous unknown natural products for aural ailment and tinnitus identified in CM that are expected to be examined in the future utilizing various aural ailment models and processes.

Lipopolysaccharide decreases cochlear blood flow dose dependently in a guinea pig animal model via TNF signaling

OBJECTIVE

To evaluate the effect of Lipopolysaccharide (LPS), a bacterial endotoxin on cochlear microcirculation, and its mode of action.

METHODS

Twenty-five Dunkin-Hartley guinea pigs were divided into five groups of five animals each. After surgical preparation, cochlear microcirculation was quantified by in vivo fluorescence microscopy. Placebo or LPS (1 mg, 10 µg, and 100 ng) was applied topically, and microcirculation was measured before and twice after application. A fifth group was pretreated with etanercept, a tumor necrosis factor (TNF) antagonist, and afterward the lowest LPS concentrations that yielded significant results (10 µg) were applied.

RESULTS

In the groups that had been treated with 1 mg and 10 µg LPS, a significant drop in cochlear microcirculation was observed after 30 (.791 ± .089 Arbitrary Units (AU), compared to baseline, and .888 ± .071AU) and 60 (.756 ± .101 AU and .817 ± .124 AU, respectively) minutes. The groups that had been treated with 100 ng LPS and that had been pretreated with etanercept showed no significant change in cochlear blood flow compared to placebo.

CONCLUSION

Lipopolysaccharide shows a dose-dependent effect on cochlear microcirculation; this effect can already be observed after 30 min. Pretreatment with etanercept can abrogate this effect, indicating that TNF mediates the effect of LPS on cochlear microcirculation.

Antioxidants and Vasodilators for the Treatment of Noise-Induced Hearing Loss: Are They Really Effective?

We live in a world continuously immersed in noise, an environmental, recreational, and occupational factor present in almost every daily human activity. Exposure to high-level noise could affect the auditory function of individuals at any age, resulting in a condition called noise-induced hearing loss (NIHL). Given that by 2018, more than 400 million people worldwide were suffering from disabling hearing loss and that about one-third involved noise over-exposure, which represents more than 100 million people, this hearing impairment represents a serious health problem. As of today, there are no therapeutic measures available to treat NIHL. Conventional preventive measures, including public awareness and education and physical barriers to noise, do not seem to suffice, as the population is still being affected by damaging noise levels. Therefore, it is necessary to develop or test pharmacological agents that may prevent and/or diminish the impact of noise on hearing. Data availability about the pathophysiological processes involved in triggering NIHL has allowed researchers to use compounds, that could act as effective therapies, by targeting specific mechanisms such as the excess generation of free radicals and blood flow restriction to the cochlea. In this review, we summarize the advantages/disadvantages of these therapeutic agents, providing a critical view of whether they could be effective in the human clinic.

Increased endothelial progenitor cell circulation and VEGF production in a rat model of noise-induced hearing loss

CONCLUSIONS

The vascular endothelial growth factor (VEGF)-mediated mechanism of endothelial progenitor cell (EPC) mobilization, migration, and differentiation may occur in response to noise-induced acoustic trauma of the cochlea, leading to the protection of cochlear function.

OBJECTIVE

The purpose of this study was to analyze changes in the cochlear vessel under an intensive noise environment.

METHODS

Sixty male Sprague-Dawley rats were randomly divided into six groups. Acoustic trauma was induced by 120 dB SPL white noise for 4 h. Auditory function was evaluated by the auditory brainstem response threshold. Morphological changes of the cochleae, the expression of VEGF, and the circulation of EPCs in the peripheral blood were studied by immunohistochemistry, Western blotting analysis, scanning electron microscopy, and flow cytometry.

RESULTS

Vascular recovery of the cochlea began after noise exposure. The change in the number of EPCs was consistent with the expression of VEGF at different time points after noise exposure. We propose that VEGF evokes specific permeable and chemotactic effects on the vascular endothelial cells. These effects can mobilize EPCs into the peripheral blood, leading the EPCs to target damaged sites and to exert a neoangiogenic effect.

Synergistic effects of free radical scavengers and cochlear vasodilators: a new otoprotective strategy for age-related hearing loss

The growing increase in age-related hearing loss (ARHL), with its dramatic reduction in quality of life and significant increase in health care costs, is a catalyst to develop new therapeutic strategies to prevent or reduce this aging-associated condition. In this regard, there is extensive evidence that excessive free radical formation along with diminished cochlear blood flow are essential factors involved in mechanisms of other stress-related hearing loss, such as that associated with noise or ototoxic drug exposure. The emerging view is that both play key roles in ARHL pathogenesis. Therapeutic targeting of excessive free radical formation and cochlear blood flow regulation may be a useful strategy to prevent onset of ARHL. Supporting this idea, micronutrient-based therapies, in particular those combining antioxidants and vasodilators like magnesium (Mg²⁺), have proven effective in reducing the impact of noise and ototoxic drugs in the inner ear, therefore improving auditory function. In this review, the synergistic effects of combinations of antioxidant free radicals scavengers and cochlear vasodilators will be discussed as a feasible therapeutic approach for the treatment of ARHL.

Effects of hypoxia on cochlear blood flow in mice evaluated using Doppler optical microangiography

Reduced cochlear blood flow (CoBF) is a main contributor to hearing loss. Studying CoBF has remained a challenge due to the lack of available tools. Doppler optical microangiography (DOMAG), a method to quantify single-vessel absolute blood flow, and laser Doppler flowmetry (LDF), a method for measuring the relative blood flow within a large volume of tissue, were used for determining the changes in CoBF due to systemic hypoxia in mice. DOMAG determined the change in blood flow in the apical turn (AT) with single-vessel resolution, while LDF averaged the change in the blood flow within a large volume of the cochlea (hemisphere with ∼1 to 1.5 mm radius). Hypoxia was induced by decreasing the concentration of oxygen-inspired gas, so that the oxygen saturation was reduced from >95% to ∼80%. DOMAG determined that during hypoxia the blood flow in two areas of the AT near and far from the helicotrema were increased and decreased, respectively. The LDF detected a decrease in blood flow within a larger volume of the cochlea (several turns averaged together). Therefore, the use of DOMAG as a tool for studying cochlear blood flow due to its ability to determine absolute flow values with single-vessel resolution was proposed.

Volumetric Imaging of Blood Flow within Cochlea in Gerbil in vivo

Changes in blood flow to the inner ear are thought to influence a number of cochlear diseases, including noise-induced hearing loss, sudden hearing loss, and Meniere's disease. Advances have been made in the areas of vital microscopic studies of micro-circulation, and the laser Doppler flowmetry. But none of these techniques can provide in vivo three-dimensional (3-D) mapping of microvascular perfusion within the cochlea. To overcome this limitation we have developed and used a method of optical microangiography (OMAG) that can generate 3-D angiograms within millimeter of tissue depths by analyzing the endogenous optical scattering signal obtained from an illuminated sample. We used OMAG to visualize the cochlear microcirculation of adult living gerbil through the intact cochlea, which would be difficult, if not impossible, by use of any other current techniques.

Role of mannitol in reducing postischemic changes in distortion-product otoacoustic emissions (DPOAEs): a rabbit model

OBJECTIVES

The aim of this study was to observe the effects of mannitol, administered topically at the round window (RW), on cochlear blood flow (CBF) and distortion-product otoacoustic emission (DPOAE) after repeated episodes of cochlear ischemia.

METHODS

Ten young rabbits were used for this study. Reversible ischemic episodes within the cochlea were induced by directly compressing the internal auditory artery (IAA). CBF was measured using a laser-Doppler (LD) probe positioned at the RW niche. DPOAEs were measured at 4, 8, and 12 kHz geometric mean frequency (GMF) using 60 dB sound pressure level (SPL) primary tone stimuli. In five test ears, mannitol was administered topically at the RW for 30 minutes before the IAA compressions. In five control ears, the IAA compressions were undertaken without application of RW medication. Each ear underwent three 5 minute IAA compressions with a 60 minute rest period between compressions.

RESULTS

In the control animals, it was observed that a progressive reduction in DPOAE level followed each successive IAA compression at all three test frequencies. The reduction in DPOAE amplitudes was consistently greater at the higher test frequencies. In the test rabbits, the RW administration of mannitol resulted in significantly less reduction in DPOAE level measures after repeated IAA compressions. For example, 30 minutes after reperfusion at 12 kHz GMF, DPOAE levels in the control ears were reduced by 1.5, 6.0, and 16 dB, compared with 1.5, 4.0, and 6.0 dB in the mannitol test ears.

CONCLUSIONS

Mannitol appears to exert a protective effect on cochlear function after periods of ischemia. The RW appears to be an efficacious route for topical administration of mannitol into the inner ear.