Impacts Of Low-frequency Vibration On Phosphorylation Of Protein Kinases And Its Safety On Human Auditory System

一、Impacts of Low-frequency Vibration on Phosphorylation Pr otein Kinases in the Inner Ear and Vestibular Nuclei of RatsObjective To evaluate the impacts of low-frequency vibration on phosphorylation of protein kinases in the inner ear and vestibular nuclei of rats.Methods 24 Sprague Dawley rats were randomly assigned into vestibular impairment-vibration, vestibular impairment-non-vibration, NaCl-vibration and NaCl-non-vibration groups. Animal model of cochleaovestibular impairment was established by transtympanic injection of 3-nitropropionic acid (3-NP), a specific inhibitor of mitochondrial respiratory complex II. The auditory function was assessed using auditory brainstem response (ABR) and the balance function was evaluated using balance beam test before transtympanic injection and 2 h and 1 d after transtympanic injection. Phosphorylation of protein kinases in the inner ear and vestibular nuclei of rats was detected using the Proteome Profiler Human Phospho-MAPK Array Kit of R&D Systems, Inc.Results All the rats showed significant hearing loss (the maximum threshold shift occurred at 12 kHz with a mean of 22.5 dB) and disequilibrium symptom after transtympanic injection 3-NP. There was no improvement in hearing but balamce function tended to recovery after low-frequency vibration treatment. Phosphorylation of protein kinase B 2 (Akt 2), cAMP response element-binding protein (CREB), extracellular signal-regulated kinases 1 (ERK1), ERK2, and c-Jun N-terminal protein kinase 1 (JNK1) in the inner ear of rats decreased markedly after intratympanic injection of 3-NP, which have the function of inducing apoptosis of the inner ear cells. Low-frequency vibration restored phosphorylation of the above protein kinases to normal level indicating an anti-apoptotic reaction.When normal animals exposed to low-frequency vibration, phosphorylation of JNK2 and p388 decreased, phosphorylation of Akt pan and JNK pan increased significantly, which indicated that shear stress induced by low-frequency vibration enhanced the resistance of cells to harmful stimulation.Phosphorylation of MAPKs in vestibular nuclei of rats after traanstympanic injection of 3-NP increased markedly, which were Aktl, Akt2, Akt3, Akt pan, CREB, ERK1, ERK2, glycogen synthase kinase-3αβ (GSK-3αβ), GSK-3β,heat shock protein 27 (HSP27), JNK1, JNK2, JNK3, MAPK kinase 3 (MKK3), MKK6, mitogen- and stress-activated kinase 2 (MSK2), p38α (MAPK14), p38δ ((MAPK13/stress-activated protein kinase (SAPK4)), p38γ (MAPK12/ERK6), p53, p70 ribosomal protein S6 kinase (p70 S6K), ribosomal s6 kinase 1 (RSK1), RSK2, and target of rapamycin (TOR). The changes might result from a compensatory response of the vestibular nuclei upon the pathological alteration of target organ (the inner ear). Phosphorylation of the above-mentioned MAPKs declined to a nearly normal level.When normal animals exposed low-frequency vibration treatment, phosphorylation of majority of MAPKs increased significantly, which might be a compensatory response of vestibular nuclei upon reduced phosphorylation of MAPKs in the target organ (the inner ear).Conclusions The regulatory mechanism of inner ear shear stress induced by low-frequency vibration is to induce the normal compensatory response of phosphorylation of the stress pathway proteins, and to enhance the resistance of normal inner ear cells and vestibular nuclei to harmful stimulation as well as increase the cell viability.二、Effects of Rotatory Low-Frequency Mastoid Vibrations on Auditory Function of Normal VolunteersObjective To evaluate the safety of a newly designed rotatory low-frequency mastoid vibration system with respect to auditory system.Methods 12 normal volunteers without vertigo were enrolled in the study, including 10 males and 2 females, aged from 23 to 25 years old. The vibrator was placed on the right mastoid process with assistance of a special holder. The vibration lasted for 30 min. Pure-tone audiography was performed on both sides before and at 30 min,1 w, and 1 y after the delivery of rotatory low-frequency vibrations. Thresholds at different frequencies at various times post-vibration delivery were compared to the thresholds before vibration exposure using the Wilcoxon signed rank test.Results At 30 min after vibration delivery, there was a significant improvement in hearing at 0.25 kHz,0.5 k, and 1 kHz in the extent of bone conduction (3,5,3 dB decrease respectively in threshold) in the ears that had been exposed to vibrations (p<0.05). At 7 days after vibration exposure, a significant decrease in the air-conduction threshold of the contralateral ears at 0.25 kHz and 0.5 kHz (p<0.05) was found. At 1 year after exposure, there were controversial changes in the exposed ears, which were that there was both a significant 6 dB decrease at 0.25 kHz and 0.5 kHz (p<0.05) and a significant 10 dB increase at 8 kHz (p<0.01) in the air conduction threshold but a significant increase at 0.25 kHz,0.5 kHz, and 1 kHz in the bone-conduction threshold (8,3,4 dB decrease respectively) (p<0.01 or 0.05, Wilcoxon test); there was a significant hearing loss at 4 kHz, and 8 kHz in the air conduction (7、10 dB decrease respectively in threshold) and at 0.25 kHz through 4 kHz in the bone conduction in the contralateral ears(7,6,6,8,8 dB decrease respectively in threshold).Conclusions There is no clear pattern in the small hearing threshold change shortly after exposure to rotatory low frequency mastoid vibration. The changes seen at 1 year after exposure are not consistent with typical vibration-induced hearing threshold change. Therefore, the rotatory low-fre-quency mastoid vibration system for vertigo therapy is safe to the auditory system.