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

Involvement of BK Channels and Ryanodine Receptors in Salicylate-induced Tinnitus

Neural hyperexcitability of the central auditory system is a key pathological characteristic of tinnitus, but its underlying molecular mechanisms remain elusive. The large-conductance Ca2+-activated K+ channel (BK) plays a crucial role in down- or upregulating neuronal activity. This study aims to investigate the role of BK channels in mediating tinnitus-associated neural hyperexcitability and elucidate the mechanisms behind it. Immunofluorescent staining revealed extensive expression of the BK channels on neurons within the central auditory system of rats. After long-term systemic administration of salicylate, a stable tinnitus inducer, we observed a significant change in the expression levels of BKα and β4 subunits in the rat central auditory system. In addition, salicylate was found to enhance the outward potassium currents mediated by the BK channel when exogenously expressed in HEK293 cells. Interestingly, this effect could be blocked by ryanodine, a potent inhibitor of ryanodine receptors (RyRs). Molecular docking identified Gln4020 within the central domain of RyR as a key residue in RyR-salicylate interactions. The results indicated that salicylate might directly activate RyRs leading to Ca2+ release from endoplasmic reticulum, and increased BK currents subsequently. Systemic treatment with paxilline, a potent blocker of BK channel, selectively reversed the increased P4/P1 amplitude ratios in the frequency region of tinnitus perception induced by single-dose salicylate administration. These results suggest that BK channels and ryanodine receptors may play a selective role in salicylate-induced tinnitus.

Molecular and behavioral effects of Acamprosate in male rats with sodium salicylate-induced tinnitus

BACKGROUND

Imbalance in inhibitory and excitatory neurotransmitters have been reported in tinnitus. Acamprosate modulates the excitatory and inhibitory neurotransmission in the nucleus accumbens (NAc). This study aims to assess the effect of Acamprosate on tinnitus, anxiety, depression, and molecular changes in nucleus accumbens (NAc), in Sodium-Salisylate (S-salicylate) model of tinnitus.

METHODS

Forty-four adult male wistar rats were used in this study. The study included Control, Saline, and S-salicylate groups during the first week, which then subdivided into five groups as Control, Saline, S-salicylate, Acamprosate, and S-salicylate+Acamprosate. Gap-in Noise (GIN) and pre-pulse inhibition (PPI) were used to assessment of tinnitus at baseline, day7 and day14. Anxiety and depression were evaluated on day 14, by elevated plus maze (EPM), open field (OF), and tail suspension (TST) tests. The protein expression of GABAAR-δ, NR1 and NR2B in NAc were also measured using western blot technique.

RESULTS

After seven days GIN reduced in S-salicylate compare to Control and Saline groups (P < 0.5), while PPI unchanged. After 14 days, GIN reduced in S-salicylate and S-salicylate+Acamprosate groups compare to Control; Saline; and Acamprosate groups (P < 0.5). Additionally, GIN was higher in S-salicylate+Acamprosate compare to S-salicylate group (P < 0.5). PPI was not changed after 14 days. Open arm time in EPM test was decreased in S-salicylate and S-salicylate+Acamprosate groups compare to Control; Saline; and Acamprosate groups (P < 0.5). Central Zone time in OF test was reduced in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5). Immobility Time in TST was increased in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5). GABAAR-δ was decreased in S-salicylate groups compare to Control, Saline, Acamprosate; and S-salicylate+Acamprosate groups (P < 0.5). NR1 and NR2B in NAc were increased in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5).

CONCLUSION

S-salicylate can induce tinnitus-like behaviors in rat. Furthermore, S-salicylate induced depression/anxiety like behaviors, and changed the expression of GABAR and NMDAR subunits in NAc. Acamprosate partially reversed these changes. In conclusion, NAc may be involved in the pathophysiologic mechanisms of tinnitus.

The Placenta as a Source of Human Material for Neuronal Repair

Stem cell therapy has the potential to meet unsolved problems in tissue repair and regeneration, particularly in the neural tissues. However, an optimal source has not yet been found. Growing evidence indicates that positive effects produced in vivo by mesenchymal stem cells (MSCs) can be due not only to their plasticity but also to secreted molecules including extracellular vesicles (EVs) and the extracellular matrix (ECM). Trophic effects produced by MSCs may reveal the key to developing effective tissue-repair strategies, including approaches based on brain implants or other implantable neural electrodes. In this sense, MSCs will become increasingly valuable and needed in the future. The placenta is a temporary organ devoted to protecting and supporting the fetus. At the same time, the placenta represents an abundant and extremely convenient source of MSCs. Nonetheless, placenta-derived MSCs (P-MSCs) remain understudied as compared to MSCs isolated from other sources. This review outlines the limited literature describing the neuroregenerative effects of P-MSC-derived biomaterials and advocates for exploiting the potential of this untapped source for human regenerative therapies.

Photobiomodulation therapy in improvement of harmful neural plasticity in sodium salicylate-induced tinnitus

Tinnitus is a common annoying symptom without effective and accepted treatment. In this controlled experimental study, photobiomodulation therapy (PBMT), which uses light to modulate and repair target tissue, was used to treat sodium salicylate (SS)-induced tinnitus in a rat animal model. Here, PBMT was performed simultaneously on the peripheral and central regions involved in tinnitus. The results were evaluated using objective tests including gap pre-pulse inhibition of acoustic startle (GPIAS), auditory brainstem response (ABR) and immunohistochemistry (IHC). Harmful neural plasticity induced by tinnitus was detected by doublecortin (DCX) protein expression, a known marker of neural plasticity. PBMT parameters were 808 nm wavelength, 165 mW/cm2 power density, and 99 J/cm2 energy density. In the tinnitus group, the mean gap in noise (GIN) value of GPIAS test was significantly decreased indicated the occurrence of an additional perceived sound like tinnitus and also the mean ABR threshold and brainstem transmission time (BTT) were significantly increased. In addition, a significant increase in DCX expression in the dorsal cochlear nucleus (DCN), dentate gyrus (DG) and the parafloccular lobe (PFL) of cerebellum was observed in the tinnitus group. In PBMT group, a significant increase in the GIN value, a significant decrease in the ABR threshold and BTT, and also significant reduction of DCX expression in the DG were observed. Based on our findings, PBMT has the potential to be used in the management of SS-induced tinnitus.