急性錳中毒對小鼠的耳毒性

Abstract

在活體外實驗中,過量的重金屬錳對於聽覺神經纖維和螺旋神經節神 經元以及耳蝸毛細胞是有毒性的,2011 年 Ding 和他的同事在神經毒 理學期刊發表的一項研究,首次顯示低濃度錳會損傷大鼠內耳的神經 元和感覺毛細胞。為了探討錳引起聽覺障礙的機制,我們評估不同劑 量的錳引起 ICR 小鼠的聽力障礙,以及對耳蝸病理損害的程度。本 研究採用聽覺腦幹誘發電位反應(ABR )記錄並且比較經過 5 次皮下 注射生理鹽水、低高劑量(10 毫克/公斤/日)或高劑量的氯化錳(50 毫克 /公斤/日) ICR 小鼠的聽覺閾值。本研究也採用免疫染色技術比較 ICR 小鼠的耳蝸內運動蛋白prestin 與凋亡蛋白cleavedcaspase-3的表達。 我們的研究結果顯示經過低和高劑量錳處理的 ICR 小鼠的 ABR 閾值 均較注射生理鹽水的 ICR 小鼠顯著增加;雖然外毛細胞的運動蛋白 prestin 表達在注射生理鹽水與錳處理的 ICR 小鼠差異不大,但是在低、 高劑量錳處理的 ICR 小鼠耳蝸內的外耳毛細胞、螺旋神經節神經元 以及血管紋細胞,均可以觀察到明顯的凋亡蛋白 cleaved caspase-3 表 達。因此,我們認為耳蝸細胞凋亡過程可能參與了錳誘導的聽覺損傷的作用。

In vitro, overdose of manganese is toxic to auditory nerve fibers as well as spiral ganglion neurons and cochlear hair cells. In 2011, Ding and his colleagues published a study in Neurotoxicology showing for the first time that low levels of manganese initially damage neurons and sensory hair cells in the inner ears of rats. To understand the mechanism for manganese-induced auditory impairment, we assessed the degree of hearing impairment and the cochlear histopathological damage in ICR mouse model resulting from various levels of manganese. The auditory brainstem response (ABR) recording was used to determine and compare the auditory threshold in ICR mice after 5 times subcutaneous injection of saline, low (10 mg/kg/day) or high dose (50 mg/kg/day) of manganese chloride. Immunochemistry staining techniques were used to compare expression of prestin, a cochlear motor protein, and cleaved caspase-3, a apoptosis protein, in the cochlea of ICR mice. Our results show that the ABR thresholds of ICR mice were significantly elevated with low and high dose of manganese treatments. Although the difference of prestin expression in outer hair cells was not observed among ICR mice with subcutaneous injection of saline, low and high dose of manganese. The apoptosis-related cleaved caspase-3 was obviously observed in outer hair cells, spiral ganglion neurons, and stria vascularis cells in the cochlea of ICR mice with subcutaneous injection low and high dose of manganese. Thus we suggest that the cochlear apoptosis may be involved in manganese-induced auditory impairment.