PO-463 Augmentation of NAD+BY NQO1 activation attenuates cisplatin-mediated hearing impairment

Abstract

IntroductionCisplatin [cis-diaminedichloroplatinum-II] is an extensively used chemotherapeutic agent, and one of its most adverse effects is ototoxicity. A number of studies have demonstrated that these effects are related to oxidative stress and DNA damage. However, the precise mechanism underlying cisplatin-associated ototoxicity is still unclear. The cofactor nicotinamide adenine dinucleotide (NAD+) has emerged as a key regulator of cellular energy metabolism and homeostasis. Although a link between NAD+-dependent molecular events and cellular metabolism is evident, it remains unclear whether modulation of NAD+ levels has an impact on cisplatin-induced hearing impairment.Material and methodsTo investigate whether augmentation of NAD+ by NQO1 activation using b-Lapachone (b-Lap) attenuates cisplatin-mediated hearing impairment, male C57BL/6 mice and NQO1 knockout mice on a C57BL/6 background were used. For analysis of the auditory threshold, auditory brainstem response (ABR) was recorded. For biochemical analysis, we measured the enzymatic activity of SIRT1, PARP1, ROS production, NAD+/NADH ratio, mRNA levels of miR-34a and pro-inflammatory cytokines. Immunohistochemistry and western blot analysis were also performed.Results and discussionsWe have demonstrated for the first time that both the protein expression level and the activity of SIRT1 were suppressed by the reduction of intracellular NAD+ levels in cisplatin-treated cochlear tissue. We also found that the decrease in SIRT1 protein expression and its activity after cisplatin exposure were mediated by the increase in transcriptional activity of p53 for miR-34a expression and PARP-1 activation causing NAD+-depletion, respectively. However, the increase in cellular NAD+ levels by NQO1 activation using b-Lap prevented mice from cisplatin-induced cochlear damage and hearing impairment through the modulation of PARP-1, SIRT1, p53, and NF-kB.ConclusionConsidering that b-Lap itself did not attenuate the tumoricidal effect of cisplatin, these results suggest that the direct modulation of the cellular NAD+ level by pharmacological agents could be a promising therapeutic strategy for enhancing the efficacy of cisplatin chemotherapy without its adverse effects.