So-Young Chang

Simultaneous bilateral laser therapy accelerates recovery after noise-induced hearing loss in a rat model

Noise-induced hearing loss is a common type of hearing loss. The effects of laser therapy have been investigated from various perspectives, including in wound healing, inflammation reduction, and nerve regeneration, as well as in hearing research. A promising feature of the laser is its capability to penetrate soft tissue; depending on the wavelength, laser energy can penetrate into the deepest part of the body without damaging non-target soft tissues. Based on this idea, we developed bilateral transtympanic laser therapy, which uses simultaneous laser irradiation in both ears, and evaluated the effects of bilateral laser therapy on cochlear damage caused by noise overexposure. Thus, the purpose of this research was to assess the benefits of simultaneous bilateral laser therapy compared with unilateral laser therapy and a control. Eighteen Sprague-Dawley rats were exposed to narrow-band noise at 115 dB SPL for 6 h. Multiple auditory brainstem responses were measured after each laser irradiation, and cochlear hair cells were counted after the 15th such irradiation. The penetration depth of the 808 nm laser was also measured after sacrifice. Approximately 5% of the laser energy reached the contralateral cochlea. Both bilateral and unilateral laser therapy decreased the hearing threshold after noise overstimulation in the rat model. The bilateral laser therapy group showed faster functional recovery at all tested frequencies compared with the unilateral laser therapy group. However, there was no difference in the endpoint ABR results or final hair cell survival, which was analyzed histologically.

Photobiomodulation by laser therapy rescued auditory neuropathy induced by ouabain

Auditory neuropathy is a hearing disorder caused by impaired auditory nerve function. The lack of information about the pathophysiology of this disease limits early diagnosis and further treatment. Laser therapy is a novel approach to enhance nerve growth or induce axonal regeneration. We induced auditory neural degeneration sparing the sensory epithelium with local ouabain application in an animal model and observed the rescue effect of photobiomodulation (PBM), showing recovered auditory function and favorable histologic outcome. Hearing was evaluated using the auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE). Seven days after ouabain application, the animals were sacrificed to evaluate the morphological changes. DPOAE change was not observed in all groups after ouabain application indicating no changes of outer hair cell function. Ouabain application increased the ABR thresholds increase, while the use of ouabain plus laser produced lower threshold compared to the ouabain group. Hematoxylin and Eosin staining of cochlea mid-modiolar sections in animals treated with ouabain showed damaged spiral ganglion cells, neurofilaments, and post synaptic puncta. Ouabain plus laser group showed higher number of spiral ganglion cells, higher density of neurofilaments, and higher number post synaptic puncta counts compared with ouabain application group. Short-term application of ouabain caused spiral ganglion cell damage while sparing the inner and outer hair cells in gerbils. Photobiomodulation alleviated the hearing loss caused by ouabain induced auditory neuropathy. The results indicate the possible role of photobiomodulation therapy for inner ear diseases accompanied by spiral ganglion degeneration.

Reinvestigation of cochlear pathology in circling mice.

The main causes of early hearing deficit in circling mice have been reported to be early degeneration of the organ of Corti and deterioration of spiral ganglion neurons. As an exact cochlear pathology is essential to explain our previous results regarding the auditory brainstem circuits of developing circling mice, we reinvestigated the cochlear pathology in developing circling mice (14, 22, and 38 days old). It has been reported that the organ of Corti in circling mice completely degenerates as early as postnatal day (P) 21 and that circling mice are deaf by P18. Although we confirmed that circling mice were deaf at P15 and that hair bundles of outer hair cells were defective at P18, complete degeneration of the organ of Corti was not observed by P38 in circling mice. At P22, the type I cell-like spiral ganglion cell density in circling mice was reduced to 78% of that of control mice (ICR mice), but it was not significantly different from that of other control mice (heterozygous (+/cir) mice, littermates of circling mice) that could hear at P22. Our data suggest that other factors, such as absence of neurotransmitter release from inner hair cells, should be considered to explain the early hearing deficit observed at P15 in circling mice.

The effect of PDT on H. influenzae biofilm in vivo

Biofilm formation has been demonstrated for many mucosal pathogens such as Haemophilus influenzae . The presence of mucosal biofilms with chronic otitis media with effusion (COME) suggests that bacteria do not clear by antibiotics. Aim: To test the effect of photodynamic therapy (PDT) on H. influenzae induced biofilm in vivo. Methods: Gerbils were divided into control (C), HI group, Laser (L), PS, PDT A, and PDT B groups. The C group received no treatment. HI group was injected with 20μl (10 8 CFU/ml) of H. influenzae into the bullae and formation of biofilms in the bullae was obtained by 5 days. For L group, 120 J/cm 2 (100 mw × 20 min) of 632 nm LD laser was irradiated by a fiber inserted into the bullae 5 days after the H. influenzae injection. For PS group, photofrin 40μl (1mg/ml) were injected into the bullae 5 days after the H. influenzae injection. PDT A group received photofrin 1 mg/ml and LD laser 120 J/cm 2 that were administered into the bullae 5 days after the H. influenzae injection. PDT B group received photofrin 2 mg/ml and laser 150 J/cm 2 5 days after the H. influenzae injection. The mucosal tissues in bullae were examined by H/E staining, and SEM. Results: The C group showed normal mucosa of bullae. The HI, L, and PS groups have shown well formed biofilm. Twenty five percent of the PDT A group and 50 % of the PDT B group have shown completely or partially resolved biofilm. Conclusion: The results of this study demonstrated that PDT appears to be effective to treat experimental H. influenzae induced biofilms in vivo. Clinical implication: PDT may be an alternative to antibiotic treatment on otitis media with biofilm formation.

Combination therapy using antioxidants and low level laser therapy (LLLT) on noise induced hearing loss (NIHL)

One of the most common factors that cause hearing disorders is noise trauma. Noise is an increasing hazard and it is pervasive, which makes it difficult to take precautions and prevent noise-induced hearing loss (NIHL). The prevalence of hearing loss among factory workers to be 42 %[1]. Ocupational noise induced hearing loss (ONIHL) continues to be a significant occupational hazard. ONIHL is permanent and may cause significant disability, for which there currently exists no cure, but is largely preventable. More than 30 million Americans are potentially exposed to hazardous noise levels in occupations such as transportation, construction, and coal mining, as well as recreationally. In the mainstream setting, exposure avoidance strategies aimed to reduce the incidence of ONIHL remain the focus of public health and occupational medicine approaches[2]. In military conditions this is most often caused by such things as explosions, blasts, or loud noises from vehicles ranging from 100 to 140 dB[3] and military weapons generating approximately 140–185 dB peak sound pressure levels[4].

Effect of low level laser therapy (LLLT) on ouabain induced auditory neuropathy in gerbils (Conference Presentation)

Aim: to investigate effectiveness of Low level laser therapy (LLLT) in rescueing ouabain induced spiral ganglion cell damage using Mongolian gerbils. Methods: Animals were divided into 3 groups; Control, Ouabain, Ouabain + LLLT group. Auditory neuropathy was induced by topical application of ouabain (1 mmol/L, 3uL) on the round window membrane in gerbils. Transmeatal LLLT was irradiated into the right ear for 1h (200mW, 720 J) daily for 7d in Ouabain + LLLT group. Before and 7 days after ouabain application, hearing was evaluated using both ABR and distortion product otoacoustic emissions (DPOAE). Seven days after ouabain application, animals were sacrificed to evaluate the morphological changes of cochlea using cochlear section image and whole mount Immunofluorescent staining. Results: DPOAE tests were normal in all animals after ouabain topical treatment indicating intact outer hair cells. Ouabain group showed ABR threshold increase compared with control group. Ouabain+LLLT group showed significant improvement of ABR threshold compared to ouabain only group. H and E stains of mid-modiolar section of cochlear showed spiral ganglion cells, neurofilaments, and post synaptic receptor counts were decreased while inner and outer hair cells were preserved in ouabain group. Ouabain +LLLT group showed higher numbers of spiral ganglion cells, density of neurofilaments and post synaptic receptor counts compared to ouabain group. Conclusions: The results demonstrated that LLLT was effective to rescue ouabain-induced spiral ganglion neuropathy.

Defining a therapeutic dosage window for transmeatal-LLLT applied to the rats with NIHL to Ameliorate NIHL

Aim: The LLLT was found to recover NIHL and ototoxicity induced hearing loss in rats but the optimal LLLT laser dosage to treat NIHL needs to be determined. The aim of this study was to find the optimal laser dosage to recover a NIHL with transmeatal-LLLT. Methods: Bilateral ears of rats were exposed to noise (narrow band noise, 120 dB, 16 kHz, 6 h). Left ears of the rats were irradiated with transmeatal-LLLT (830 nm) of 50, 100, 150, 200, 250, 300 mW for 60 minutes per day for 12 days, starting 1 day post induction of NIHL. Right ears were not irradiated and used as control ears. The hearing levels were measured at each frequency of 8, 12, and 32 kHz before the noise exposure, 1, 3, 8, and 12 days post noise exposure. The differences of hearing levels between left treated ear and right controlled ear at each frequency of different laser dosages (50 – 300 mW) were compared to see the most effective laser dosages to treat NIHL. Results: Hearing levels were most improved by 150 mW, slightly improved by 200 mW, not improved by 50 and 250 mW, and became worse by 300 mW. Conclusion: The results of this study suggest that most effective therapeutic laser dosage window to treat NIHL with transmeatal-LLLT was 150 mW for 12 days and it was not effective by 50, 250, and 300 mW.

Effect of LLLT on the level of ATP and ROS from organ of corti cells

It is well established that ototoxic antibiotics and acoustic trauma can damage cochlear hair cells and cause hearing loss. Previous studies using transcanal LLLT (Low level laser therapy) showed that LLLT can promote recovery of hearing thresholds and cochlear hair cells. However, its mechanism has not been studied. Aim: The aim of this study is to investigate the mechanism of hearing recovery from gentamicin induced ototoxic hearing loss by LLLT. Methods: HEI- OC1 (House ear institute organ of Corti) cells were cultured for 18 hours and ototoxicity was induced by gentamicin (GM) treatment to the cells. Cultured cells were divided into 6 groups, No treatment control, LLLT only, GM 6.6 mM and GM 13.1 mM, GM 6.6 mM+LLLT and GM 13.1 mM+LLLT cells. LD laser 808 nm, 15 mW, was irradiated to the cultured cells for 15 min, at 4 hours after GM treatment to the cells. ATP was assayed using the ATP assay Kit. ROS was measured using confocal microscope after application of H2DCFDA dye. Results: ATP was decreased in GM 13.1 mM cells and increased in LLLT only cells and GM 13.1 mM+LLLT cells compared to control and 13.1 mM cells. ROS was increased in GM 6.6 mM and GM 13.1 mM cells, and decreased in GM 6.6 mM+LLLT and GM 13.1 mM+LLLT cells compared to GM 6.6 and 13.1 mM cells immediately after laser irradiation. Conclusion: This study demonstrated that LLLT on GM treated HEI-OC1 cells increased ATP and decreased ROS that may contribute to the recovery of hearing.

The optimal window time to treat noise-induced hearing loss (NIHL) with low level laser therapy (LLLT)

The transcanal LLLT was found to recover noise induced hearing loss (NIHL) but the LLLT was performed immediately after the induction of NIHL. The aim of this study was to find an optimal window time to treat and recover a NIHL with LLLT. Bilateral ears of 6SD rats (12ears) were exposed to noise. Left ears of the rats were irradiated with a LLLT (830 nm, 594 J/cm2 per day) for 12 days, starting 3 days and 7 days post exposure to noise. Right ears were used as control ears. The hearing levels were measured at each frequency of 4, 8, 12, 16, and 32 kHz before and after the noise exposure and post 12th irradiations. The initial hearing levels in all frequencies before and after the noise exposure were 26.5, 24.5, 24.0, 24.0 and 24.5 dB SPL and 63.5, 64, 71.5, 73.5 and 67.5 dB SPL in 4, 8, 12, 16 and 32 kHz, respectively in 6 ears. After 12th irradiation, the thresholds of the LLLT treated left ears of the 3-day group recovered significantly compared to those of the untreated right. However, for the 7 day group, the recovery of the LLLT treated left ears was not significantly improved compared to that of the untreated right. The results of this study suggest that the optimal window time to treat NIHL with LLLT was within 3 days from the exposure to noise but the hearing failed to recover if the LLLT was started 7 days post exposure to noise.