Photobiomodulation Can Enhance Stem Cell Viability in Cochlea with Auditory Neuropathy but Does Not Restore Hearing

Figure 3

Auditory function after combination therapy with mouse embryonic stem cells (mESCs) and photobiomodulation (PBM) in a secondary neurodegeneration model. (a) Scheme for combination therapy with mESCs and PBM: Secondary neurodegeneration was induced in adult C57BL/c6 mice using kanamycin (KM). Green fluorescent protein (GFP)-tagged mESCs were transplanted into the cochlea, followed by near-infrared (NIR)-PBM irradiation of the cochlea, at 8 weeks after KM surgery. For PBM, an NIR laser with a wavelength of 808 nm was used to irradiate the cochlea through the tympanic membrane for 5 days. The mESCs were transplanted into the round window (RW) of the cochlea at 8 weeks after KM surgery, and assessment was performed at 1 and 2 weeks after the combination therapy. Hearing was evaluated by measuring auditory brainstem responses (ABRs) before and 2, 4, and 8 weeks after KM treatment and 1 and 2 weeks after combination therapy (9 and 10 weeks after KM treatment). (b) ABRs at 2 weeks after combination therapy (10 weeks after KM surgery). The ABR thresholds had increased in all groups at all frequencies (8, 16, and 32 kHz), reflecting no hearing improvement. (c) Electrical auditory brainstem responses (eABRs) at 2 weeks after combination therapy. Relative to baseline, no eABR waveform appeared, confirming the lack of nerve regeneration.

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