The human neuroprotective placental protein composition suppressing tinnitus and restoring auditory brainstem response in a rodent model of sodium salicylate-induced ototoxicity

Abstract

The effect of neuroprotective placental protein composition (NPPC) on the suppression of tinnitus and the restoration of the auditory brainstem response (ABR) characteristics was explored in tinnitus-induced rats. The animals were placed into two groups: (1) the study group, rats received sodium salicylate (SS) at the dose of 200 mg/kg twice a day for two weeks, and then 0.4 mg of the NPPC per day, between the 14th and 28th days, (2) the placebo group, rats received saline for two weeks, and then the NPPC alone between the 14th and 28th days. The gap pre-pulse inhibition of the acoustic startle (GPIAS), the pre-pulse inhibition (PPI), and the ABR assessments were performed on animals in both groups three times (baseline, day 14, and 28). The GPIAS value declined after 14 consecutive days of the SS injection, while NPPC treatment augmented the GPIAS score in the study group on the 28th day. The PPI outcomes revealed no significant changes, indicating hearing preservation after the SS and NPPC administrations. Moreover, some changes in ABR characteristics were observed following SS injection, including (1) higher ABR thresholds, (2) lowered waves I and II amplitudes at the frequencies of 6, 12, and 24 kHz and wave III at the 12 kHz, (3) elevated amplitude ratios, and (4) prolongation in brainstem transmission time (BTT). All the mentioned variables returned to their normal values after applying the NPPC. The NPPC use could exert positive therapeutic effects on the tinnitus-induced rats and improve their ABR parameters.

Keywords: Auditory; Auditory brain stem response; Evoked potentials; Placental extract; Tinnitus.

The graphical summary of this study.

Fig. 1

Experimental design and timelines for the course of the experiment on two animal groups SS stands for sodium salicylate.

Fig. 2

Acoustic Startle Response (ASR) setup: A behavioral test to assess GPIAS and PPI in rats. The rats were placed in a sound-attenuating chamber on a piezoelectric platform, which was kept inside a plastic holder. The sounds were delivered through two loudspeakers placed on the ceiling of the room, one for background noise and the other for the presentation of the startle stimuli. The arrows show different parts of the setup.

Fig. 3

Auditory Brainstem Response (ABR) Recording Setup. (A) Auditory Lab System, (B) The figure indicates how to perform the ABR test protocol in a rat. The loudspeakers and electrons are shown with arrows. (C) Three subdermal needle electrodes were placed at the vertex (noninverting) and under the left mastoid (inverting) and the right (ground) ear.

Fig. 4

An example of the baseline, post-SS (day 14), and post-NPPC (day 28) administration ABR recordings. Note the decrease in the amplitude responses compared to the baseline recordings and after the NPPC. The BTT is also considered as the interval between the peak waves I–V.

Fig. 5

GPIAS and PPI measurement results (A) The effects of the SS and the NPPC on the GPIAS values. The chronic study group indicated a significant decrease in the GPIAS values compared with the baseline and the control group. Asterisks (*) represent the significance between the control and chronic study groups, while the triangles (Δ) show significant value differences within each group. (B) The effects of the SS on the PPI values. No significant differences were seen in the PPI values between both study groups (p > 0.05).

Fig. 6

The effects of the SS and the NPPC on the ABR hearing threshold shift in both study groups (A) The waveforms of the ABRs compared at the baseline, tinnitus (day 14), and NPPC administration (day 28). The arrows indicate the hearing threshold. (B) The summary of the averaged ABR thresholds at various frequencies of 6, 12, and 24 KHz. The asterisks (*) represent the pairwise comparisons within the control and chronic study groups (p < 0.05).

Fig. 7

The effects of the SS and the NPPC on the ABR amplitude shift in the rats. The amplitude shift were determined using 6, 12 and 24 kHz tone burst stimulations (n = 8), calculated before the SS administration (baseline), the day 14 after the SS administration (the day 14), and day 14 after the SS + NPPC administration (the day 28). (A) Amplitude of wave I (B) amplitude of wave II (C) amplitude of wave III (D) amplitude of wave IV (E) amplitude of wave V. The statistical significance level was considered as (p < 0.05).

Fig. 8

The effects of the SS and the NPPC on the ABR absolute latency shift in the rats (n = 8). The absolute latency shifts were determined using 6, 12 and 24 kHz tone burst stimulations, calculated before the SS administration (baseline), after the SS administration (day 14), and the day 14 after the SS + NPPC administration (day 28). (A) Absolute latency shift of peak I (B) absolute latency shift of peak II (C) absolute latency shift of peak III (D) absolute latency shift of peak IV (E) absolute latency shift of peak V.

Fig. 9

The effects of the SS and the NPPC on the ABR amplitude ratios in the rats (n = 8). The amplitude ratios were determined using 6, 12 and 24 kHz tone burst stimulations, calculated before the SS administration (baseline), after the SS administration (day 14), and day 14 after the SS + NPPC administration (day 28). (A) Amplitude ratio of waves II/I (B) Amplitude ratio of waves V/I (C) Amplitude ratio of waves IV/I.

Fig. 10

BTT results. The effects of the SS and the NPPC on the BTT values. The chronic study group indicated a significant increase in the BTT values on day 14 (the SS injection) compared with the baseline, while the BTT value dropped after the NPPC administration on day 28 compared to that on day 14. (A) BTT of 6 KHz (B) BTT of 12 KHz (C) BTT of 24 KHz. Asterisks (*) represent the significance between the control and chronic study groups, whereas the triangles (Δ) show significant value differences within each group (p < 0.05).