以動物模式探討糖尿病影響噪音性聽力損失

Using animal model to investigate diabetic impact on noise induced hearing loss

吳弘斌(Hung-Pin Wu)

指導教授 ： 郭育良

共同指導教授 ： 鄭尊仁 ； 許權振

國立臺灣大學/公共衛生學院/職業醫學與工業衛生研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.02876

摘要

糖尿病與噪音性聽力損失均是影響健康與生活品質的重要因素，病理與動物研究顯示兩者之間是有可能互相影響的，然而在流行病學觀察型研究卻有著爭議，本研究打算以動物模式來探討兩者之間的關係：1. 探討糖尿病是否會影響暫時性噪音性聽力損失的恢復；2. 探討糖尿病是否會使永久性噪音性聽力損失更嚴重及聽力保護藥物於糖尿病鼠的功能；3. 探討糖尿病於聽覺傳導路徑的影響。
第一部分，先探討糖尿病是否會影響暫時性噪音性聽力損失的恢復。28隻雄性Wistar鼠，分為三組：控制組 (C), 糖尿病有胰島素治療組(DI), 糖尿病沒有胰島素治療組(DM)。使用Streptozotocin來誘發老鼠產生糖尿病，所有鼠均暴露於110分貝噪音下達八小時，腦幹聽性誘發反應和歪成耳聲傳射檢查、 在噪音暴露前一天的資料作為基準值，並於噪音暴露後一小時、一天、兩天、四天、七天和十四天後再測。發現腦幹聽性誘發反應和歪成耳聲傳射檢查、在C組第一天就恢復，DM組第十四天才恢復，而DI組則介於兩者之間，本實驗建議糖尿病人需要合適的血糖控制及更周全的保護來對抗噪音。
第二部分，探討經由反覆的噪音暴露，糖尿病是否會使永久性噪音性聽力損失更嚴重及N-acetylcysteine (NAC)一種抗氧化劑的前驅物，是否會使糖尿病鼠的噪音性聽力損失減少。50隻雄性Wistar鼠，分為四組：12隻打生理食鹽水的控制組 (Control-Saline), 11 隻打NAC的控制組(Control-NAC), 13隻打生理食鹽水的糖尿病組(Diabetes-Saline) and 14隻打NAC的糖尿病組(Diabetes-NAC)。NAC (325 mg/kg) 每天兩次腹腔注射，從噪音暴露前兩天開始，連續十四天，所有鼠均暴露於110分貝噪音下達八小時，連續十天以產生永久性噪音性聽力損失。腦幹聽性誘發反應分別在噪音暴露前，與後一小時、一週、兩週與四週後量測，之後將鼠的耳蝸取下，於光學顯微鏡下計算耳蝸毛細胞的數目。結果於四週後，Diabetes-Saline的聽力損失最嚴重達36.9 ± 2.3 分貝，Control-Saline 和 Diabetes-NAC 次之， Control-NAC最少為19.5 ± 2.0分貝，此外耳蝸圖發現僅有Diabetes-Saline的外毛細胞有相當程度的損失。
第三部分，探討(1) compromised medial olivocochlear bundle (MOCB) activities and腦幹聽性誘發反應(ABR)的時間進程和(2) 胰島素於糖尿病相關聽覺障礙的影響。30隻雄性Wistar鼠，分為三組：控制組 (C), 糖尿病有胰島素治療組(DI), 糖尿病沒有胰島素治療組(DM)。每月測量ABR、歪成耳聲傳射檢查、歪成耳聲傳射檢查的對側抑制。在研究期間，各組的聽力均無明顯上升，但DM組在第二十九週時的腦幹聽性誘發反應wave III與I-III有延長(p<0.05)、在第二十五週時歪成耳聲傳射檢查的對側抑制有明顯下降的現象，但C與DI組均無此現象，也就是說糖尿病鼠在ABR尚未出現明顯變化前， 歪成耳聲傳射檢查的對側抑制有明顯下降的現象， Compromised medial olivocochlear bundle (MOCB) activities的時間進程與糖尿病的時間有正相關且胰島素有保護的作用。
總結起來：(1)糖尿病會減慢暫時性噪音性聽力損失的恢復；(2) 糖尿病會使永久性噪音性聽力損失更嚴重，此外NAC會保護內耳外毛細胞並同時減緩糖尿病鼠與非糖尿病鼠的噪音性聽力損失；(3) 歪成耳聲傳射檢查的對側抑制比腦幹聽性誘發反應更適合做為糖尿病相關聽力損失的早期指標。

關鍵字

糖尿病 ； 噪音性聽力損失 ； 腦幹聽性誘發反應 ； 歪成耳聲傳射檢查 ； 對側抑制

並列摘要

Diabetes and noise induced hearing loss (NIHL) are both very common conditions affecting the health and quality of life. The pathologic and animal studies suggest plausible biologic interactions between diabetes and noise. However, in epidemiologic observational studies revealed controversial results. The purpose of this study is to investigate 1. whether diabetes impairs the recovery from noised-induced temporary hearing loss; 2. whether diabetes exaggerates permanent threshold shifts and the role of otoprotective agents in diabetic rats.; 3. the possible mechanism interacts between diabetes and auditory pathway.
In the first part of the study, we try to investigate whether diabetes impairs the recovery from noised-induced temporary hearing loss. Twenty-eight male Wistar rats were divided into three groups: control (C), diabetes with insulin control (DI), and diabetes without insulin control (DM). Diabetes was induced by intraperitoneal injection of streptozotocin. All animals were exposed to white noise at 110dB SPL for eight hours. Auditory brainstem response (ABR) thresholds and distortion product otoacoustic emission (DPOAE) amplitudes were measured for all animals one day prior to noise exposure, to obtain a baseline for hearing function, and then one hour, one day, two days, four days, seven days, and 14 days after noise exposure. One hour post exposure, ABR thresholds shifted markedly, and DPOAE was reduced similarly in all groups. Both ABR thresholds and DPOAE returned to the baseline in the control group at day 1, but they were not back to the baseline in the DM group even by day 14. Compared with the control group, the ABR threshold shifts and DPOAE returned to baseline more slowly in the DI group. The present study suggests that diabetic patients need proper blood sugar control and probably need more effective preventive measures to preserve their hearing from the effects of noise.
In the second part of the study, we try to investigate whether repeated noise exposure aggravates the level of permanent noise-induced hearing loss (NIHL) in diabetic rats and whether N-acetylcysteine (NAC), a precursor of glutathione, attenuates the level of noise-induced permanent hearing loss in diabetic rats. Fifty male Wistar rats were divided into four groups: 12 non-diabetic control rats with saline injection (Control-Saline), 11 non-diabetic control rats with NAC injection (Control-NAC), 13 streptozotocin-induced diabetic rats with saline injection (Diabetes-Saline) and 14 streptozotocin-induced diabetic rats with NAC injection (Diabetes-NAC). NAC (325 mg/kg) was given by intraperitoneal injection twice per day (b.i.d.) for 14 days starting 2 days before noise exposure. All rats were exposed to noise for 8 hours per day for 10 consecutive days to develop noise-induced permanent hearing loss. The hearing status of all animals was evaluated with auditory brainstem responses (ABR) evoked by clicks and tone bursts. ABRs were measured before and at 1 hour, 1 week, 2 weeks and 4 weeks after noise exposure. After a recovery time of 4 weeks, animals were decapitated, and the loss of hair cells was assessed microscopically. In all groups, ABR thresholds failed to return to pre-exposure values throughout the experimental period. The ABR threshold to clicks was markedly elevated in the Diabetes-Saline group (36.9 ± 2.3 dB SPL), less elevated in the Control-Saline and Diabetes-NAC groups and least in the Control-NAC group (19.5 ± 2.0 dB SPL) at 4 weeks after noise exposure. Diabetes caused increased susceptibility to noise-induced hearing loss, and NAC treatment reduced the loss in both control and diabetic rats. Cochleograms revealed no gross destruction of hair cells in the non-diabetic groups or the Diabetes-NAC group; however, a significant number of outer hair cells (OHCs) were lost in the Diabetes-Saline group.
In the third part of the study, we try to investigate in diabetic rats: (1) the evolution of compromised medial olivocochlear bundle (MOCB) activities and auditory brainstem responses (ABR), and (2) the insulin effect on diabetes-related hearing dysfunction. Thirty male Wistar rats were divided into three groups: control (C), diabetes with insulin injection (DI), and diabetes without insulin injection (DM). Click-evoked ABR, distortion product otoacoustic emission (DPOAE) and the contralateral suppression of DPOAE were measured for all animals monthly. Chronological changes of thresholds of click-evoked ABR in each group were presented without statistical significance among the groups. Wave III was delayed and interpeak latency I-III was prolonged in the DM group at the age of 29 weeks (p<0.05). The amplitudes of the contralateral suppression of DPOAE were markedly decreased after the 25th week in the DM group, but not in the C and DI groups. Compared to the C group, contralateral suppression in the DI group was not compromised through all frequencies. Dysfunction of the auditory efferent olivocochlear activities developed in diabetic subjects presenting no evidence of hearing loss. The clinical finding of a significant decrease of contralateral suppression of DPOAE could be used as an earlier indicator of diabetes-related hearing impairment than the changes of ABRs. The evolution of compromised MOCB is positively related with the duration of diabetes, and insulin could play the protective effect on it.
In summary, we conclude that in Wistar rats (1) diabetes may delay the recovery from noise induced temporary hearing loss； (2) diabetics are prone to developing more severe permanent NIHL than non-diabetics and NAC could preserve most OHCs and attenuate the permanent noise-induced hearing loss in both groups；(3) contralateral suppression of DPOAE could be used as an earlier indicator of diabetes-related hearing impairment than the changes of ABRs.

並列關鍵字

diabetes ； noise induced hearing loss ； auditory brainstem response ； distortion product otoacoustic emissions ； contralateral suppression

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