Carboxy alkyl esters of Uncaria tomentosa augment recovery of sensorineural functions following noise injury

Abstract

This study tested the hypothesis that hydrophilic chemotypes of the medicinal vine Uncaria tomentosa ( UT) would facilitate recovery of sensorineural functions following exposure to a damaging level of noise. The particular chemotypes investigated were carboxy alkyl esters (CAE) which are known to exhibit multifunctional cytoprotective properties that include: enhanced cellular DNA repair, antioxidation and anti-inflammation. Long–Evans rats were divided into four treatment groups: vehicle-control, noise-only, CAE-only and CAE + noise. The noise exposure was an 8 kHz octave band of noise at 105 dB SPL for 4 h. Outer hair cell (OHC) function was measured with the cubic 2 f 1– f 2 distortion product otoacoustic emissions (DPOAE) at the start of the study (baseline) and at time-points that corresponded to 1 day, 1 week and 4 weeks post-noise exposure to determine within-group effects. Compound action potentials to puretone stimuli were recorded from the VIIIth craniofacial nerve at 4 weeks post-noise exposure to determine between-group effects. Additionally, cytocochleograms were constructed for each row of OHCs from each group. Noise exposure produced significant sensorineural impairments. However, CAE treatment facilitated almost complete recovery of OHC function and limited the magnitude of cell loss. The loss of neural sensitivity to puretone stimuli was inhibited with CAE treatment. Therefore, it appears that the multifunctional cytoprotective capacity of CAE from UT may generalize to otoprotection from acoustic over-exposure.