Fay and Carl Simons Center for Biology of Hearing and Deafness, Department of Otolaryngology, Washington University School of Medicine, 660 S. Euclid, St. Louis, MO 63110, USA.
Hear Res. 2011 Oct;280(1-2):141-7. doi: 10.1016/j.heares.2011.05.007. Epub 2011 May 27.
We recently demonstrated that sub-chronic low-dose kanamycin (KM, 300 mg/kg sc, 2×/day, 10 days) dramatically reduces permanent noise-induced hearing loss (NIHL) and hair cell loss in 1 month old CBA/J mice (Fernandez et al., 2010, J. Assoc. Res. Otolaryngol. 11, 235-244). Protection by KM remained for at least 48 h after the last dose, and appeared to involve a cumulative effect of multiple doses as part of a preconditioning process. The first month of life lies within the early 'sensitive period' for both cochlear noise and ototoxic injury in mice, and CBA/J mice appear exquisitely vulnerable to noise during this period (Ohlemiller et al., 2011; Hearing Res. 272, 13-20). From our initial data, we could not rule out 1) that less rigorous treatment protocols than the intensive one we applied may be equally-or more-protective; 2) that protection by KM is tightly linked to processes unique to the sensitive period for noise or ototoxins; or 3) that protection by KM is exclusive to CBA/J mice. The present experiments address these questions by varying the number and timing of fixed doses (300 mg/kg sc) of KM, as well as the age at treatment in CBA/J mice. We also tested for protection in young C57BL/6J (B6) mice. We find that nearly complete protection against at least 2 h of intense (110 dB SPL) broadband noise can be observed in CBA/J mice at least for ages up to 1 year. Reducing dosing frequency to as little as once every other day (a four-fold decrease in dosing frequency) appeared as protective as twice per day. However, reducing the number of doses to just 1 or 2, followed by noise 24 or 48 h later greatly reduced protection. Notably, hearing thresholds and hair cells in young B6 mice appeared completely unprotected by the same regimen that dramatically protects CBA/J mice. We conclude that protective effects of KM against NIHL in CBA/J mice can be engaged by a wide range of dosing regimens, and are not exclusive to the sensitive period for noise or ototoxins. While we cannot presently judge the generality of protection across genetic backgrounds, it appears not to be universal, since B6 showed no benefit. Classical genetic approaches based on CBA/J × B6 crosses may reveal loci critical to protective cascades engaged by kanamycin and perhaps other preconditioners. Their human analogs may partly determine who is at elevated risk of acquired hearing loss.
我们最近的研究表明，亚慢性低剂量卡那霉素（KM，300mg/kg sc，2 次/天，10 天）可显著减少 1 个月大的 CBA/J 小鼠的永久性噪声诱导听力损失（NIHL）和毛细胞损失（Fernandez 等人，2010 年，J. Assoc. Res. Otolaryngol. 11，235-244）。KM 的保护作用至少在最后一次给药后持续 48 小时，并且似乎涉及多次剂量的累积效应，作为预处理过程的一部分。生命的第一个月处于耳蜗噪声和耳毒性损伤的早期“敏感期”，而 CBA/J 小鼠在此期间对噪声极为敏感（Ohlemiller 等人，2011 年；Hearing Res. 272，13-20）。从我们最初的数据来看，我们不能排除以下可能性：1）与我们应用的强化治疗方案相比，不太严格的治疗方案可能同样具有保护作用，或者更具保护作用；2）KM 的保护作用与噪声或耳毒性敏感期特有的过程紧密相关；或 3）KM 的保护作用仅对 CBA/J 小鼠具有特异性。本实验通过改变亚慢性低剂量 KM（300mg/kg sc）的剂量和次数以及 CBA/J 小鼠的治疗年龄，来研究这些问题。我们还在年轻的 C57BL/6J（B6）小鼠中测试了保护作用。我们发现，在 CBA/J 小鼠中，至少在 1 岁之前，至少 2 小时的高强度（110dB SPL）宽带噪声可以观察到几乎完全的保护作用。将给药频率降低至每天一次（给药频率降低四倍）与每天两次给药一样具有保护作用。然而，将剂量减少到 1 或 2 次，然后在 24 或 48 小时后进行噪声处理，大大降低了保护作用。值得注意的是，年轻的 B6 小鼠的听力阈值和毛细胞似乎完全不受同样对 CBA/J 小鼠具有显著保护作用的方案的保护。我们得出的结论是，KM 对 CBA/J 小鼠的 NIHL 的保护作用可以通过广泛的给药方案来实现，并且不仅仅局限于噪声或耳毒性的敏感期。虽然我们目前无法判断保护作用在遗传背景上的普遍性，但它似乎不是普遍存在的，因为 B6 没有受益。基于 CBA/J×B6 杂交的经典遗传方法可能会揭示与 KM 及其他预处理剂相关的保护级联途径的关键基因座。它们的人类类似物可能部分决定了谁处于获得性听力损失的高风险中。
