N-Acetyl-L-cysteine Affects Ototoxicity Evoked by Amikacin and Furosemide Either Alone or in Combination in a Mouse Model of Hearing Threshold Decrease

Abstract

Drug-induced ototoxicity resulting from therapy with aminoglycoside antibiotics and loop diuretics is one of the main well-known causes of hearing loss in patients. Unfortunately, no specific protection and prevention from hearing loss are recommended for these patients. This study aimed at evaluating the ototoxic effects produced by mixtures of amikacin (AMI, an aminoglycoside antibiotic) and furosemide (FUR, a loop diuretic) in the mouse model as the hearing threshold decreased by 20% and 50% using auditory brainstem responses (ABRs). Ototoxicity was produced by the combinations of a constant dose of AMI (500 mg/kg; i.p.) on FUR-induced hearing threshold decreases, and a fixed dose of FUR (30 mg/kg; i.p.) on AMI-induced hearing threshold decreases, which were determined in two sets of experiments. Additionally, the effects of N-acetyl-L-cysteine (NAC; 500 mg/kg; i.p.) on the hearing threshold decrease of 20% and 50% were determined by means of an isobolographic transformation of interactions to detect the otoprotective action of NAC in mice. The results indicate that the influence of a constant dose of AMI on FUR-induced hearing threshold decreases was more ototoxic in experimental mice than a fixed dose of FUR on AMI-induced ototoxicity. Moreover, NAC reversed the AMI-induced, but not FUR-induced, hearing threshold decreases in this mouse model of hearing loss. NAC could be considered an otoprotectant in the prevention of hearing loss in patients receiving AMI alone and in combination with FUR.

Keywords: N-acetyl-cysteine; amikacin; furosemide; hearing loss; hearing threshold decrease; ototoxicity.

Figure 1

Effects of NAC, FUR and their combinations on AMI-induced hearing threshold decrease in mice. The dose–response relationship curves for AMI-induced hearing threshold decrease of 20% (A) and 50% (C) are plotted graphically, from which the HTDD₂₀ and HTDD₅₀ values (for AMI administered alone and in combination with FUR, NAC, and both compounds) were calculated. The HTDD₂₀ (B) and HTDD₅₀ (D) values were statistically analyzed with one-way ANOVA followed by Holm–Sidak’s multiple comparisons tests. * p < 0.05, ** p < 0.01 and *** p < 0.001 vs. AMI+VEH-treated animals; ## p < 0.01 and #### p < 0.0001 vs. AMI+NAC-treated animals; @ p < 0.05 vs. AMI+FUR-treated animals; NAC—N-acetylcysteine; AMI—amikacin; FUR—furosemide; NS—nonsignificant; VEH—vehicle.

Figure 2

Effects of NAC, AMI and their combinations on FUR-induced hearing threshold decrease in mice. Dose–response relationship curves for FUR-induced hearing threshold decrease of 20% (A) and 50% (C) are plotted graphically, from which the HTDD₂₀ and HTDD₅₀ values (for FUR administered alone and in combination with AMI, NAC, and both compounds) were calculated. The HTDD₂₀ (B) and HTDD₅₀ (D) values were statistically analyzed with one-way ANOVA followed by Holm–Sidak’s multiple comparison tests. * p < 0.05 vs. FUR+VEH-treated animals; # p < 0.05 and ## p < 0.01 vs. FUR+NAC-treated animals. NAC—N-acetylcysteine; AMI—amikacin; FUR—furosemide; NS—nonsignificant; VEH—vehicle.

Figure 3

Isobolographic transformation of interaction between AMI and FUR in the drug-induced hearing threshold decrease of 20% and 50% in mice. Doses of AMI and FUR are plotted on the X- and Y-axes, respectively. The dotted line parallel to the Y-axis represents a constant dose of AMI (a,b) or FUR (c,d), which was added to the increasing doses of FUR or AMI in the mouse model of a hearing threshold decrease of 20% and 50%, respectively. Point A (on each graph) illustrates the theoretically additive dose of the two-drug mixture (AMI+FUR) that could produce a hearing threshold decrease of 20% or 50%, respectively. Point B indicates the dose of AMI and FUR that experimentally evoked a hearing threshold decrease of 20% and 50%, respectively. Point C illustrates the dose of the two-drug mixture producing a hearing threshold decrease of 20% and 50% in animals exposed additionally to NAC (500 mg/kg). * p < 0.05, ** p < 0.01, *** p < 0.001 and **** p < 0.0001 vs. the respective treatment group. NAC—N-acetylcysteine; AMI—amikacin; FUR—furosemide.