siRNA-mediated knock-down of NOX3: therapy for hearing loss?

Abstract

Cisplatin is a widely used chemotherapeutic agent that causes significant hearing loss. Previous studies have shown that cisplatin exposure is associated with increase in reactive oxygen species (ROS) in the cochlea. The inner ear expresses a unique isoform of NADPH oxidase, NOX3. This enzyme may be the primary source of ROS generation in the cochlea. The knockdown of NOX3 by pretreatment with siRNA prevented cisplatin ototoxicity, as demonstrated by preservation of hearing thresholds and inner ear sensory cells. Trans-tympanic NOX3 siRNA reduced the expression of NOX3 and biomarkers of cochlear damage, including transient receptor vanilloid 1 (TRPV1) channel and kidney injury molecule-1 (KIM-1) in cochlear tissues. In addition, siRNA against NOX3 reduced apoptosis as demonstrated by TUNEL staining, and prevented the increased expression of Bax and abrogated the decrease in Bcl2 expression following cisplatin administration. Trans-tympanic administration of siRNA directed against NOX3 may provide a useful method of attenuating cisplatin ototoxicity. In this paper, we review recent publications dealing with the role of NOX3 in ototoxicity and the effects of siRNA against cisplatin-induced hearing loss.

Fig. 1

Trans-tympanic injection of siRNA against NOX3 abrogates cisplatin-induced hearing loss in rat. a Pretreatment Auditory Brainstem Responses (ABRs) were recorded in naïve rats which were then administered scrambled siRNA (scramble) or siRNA against NOX3 (siNOX3). Cisplatin (11 mg/kg, intraperitoneally) was injected 48 h after siRNA administration. Post-treatment ABR thresholds were recorded 3 and 5 days after cisplatin administration and compared to pretreatment values. ABR threshold measured 3 days after scramble plus cisplatin showed a 35.5 ± 5 dB elevation which was reduced in a dose-dependent manner by siRNA against NOX3. b Scanning electron microscopy (SEM) of the basal turn of the cochlea showed protection of OHCs from cisplatin-induced damage by siRNA against NOX3 (siNOX3). Trans-tympanic injection of 0.6 μg of siRNA against NOX3 48 h prior to cisplatin administration protected OHCs from cisplatin-induced damage. SiNOX3 alone (0.6 μg) did not damage OHCs. Arrows indicate damaged OHCs. c Assessment of damage to OHCs by cisplatin from SEM images. Cisplatin damaged about 50  % of OHCs (scramble + cisplatin) group which was abrogated by trans-tympanic administration of 0.6 μg of siRNA against NOX3 (siNOX3). All experiments were repeated at least eight times. Asterisk (*) denotes statistically significant difference from the siNOX3 (0.6 μg) group, while (**) indicates significant differences between the scramble + cisplatin and siNOX3 (0.6 μg) + cisplatin treatment groups. Statistical significance was determined using the Students t test and assessed at the p < 0.05 level [32]. (Republished with permission from Mary Ann Liebert, New Rochelle, NY 10801–5215, USA)

Fig. 2

Flow chart showing various potentially harmful drugs, agents, or processes that could activate NOX3 in the cochlea, leading to excess ROS production, damage to cochlear tissues, resulting in cell death and hearing loss. It may be possible to protect the cochlea against some of these damaging influences by inhibition of NOX3, such as by administration of siRNA against NOX3