Researchers in New Zealand have found that a new drug can restore hearing after carrying out research on noise-induced hearing loss in rats.

Drug therapies for noise-induced hearing loss have only recently been proposed and, to date, there are no treatments that can repair the damage to the inner ear and reduce the impact of hearing loss. Researchers from the University of Auckland, New Zealand, have now found that a potent new drug restores hearing after noise-induced hearing loss in rats.

We are exposed to noise at work, to traffic noise in the street and when we listen to music or go to night clubs or concerts where the volume is too loud. Noise exposure and intense sounds can cause hearing loss and tinnitus.

The researchers found that injections of an agent called 'ADAC' (adenosine amine congener) activates adenosine receptors in cochlear tissues, resulting in recovery of hearing functions. Adenosine plays an important role in biochemical processes, such as energy transfer. The findings may pave the way for effective non-surgical therapies to restore hearing loss after noise-induced injury.

ADAC or placebo

In the study, rats were exposed to narrow-band noise for 2 to 24 hours in an acoustic chamber to induce cochlear damage and permanent hearing loss. ADAC or placebo was then injected into the belly of the rats. The researchers measured the hearing in the rats before and after the treatments using a technique known as auditory brainstem response (ABR). They also used histological techniques to determine the number of missing cochlear sensory hair cells after noise exposure and the noise-induced production of free radicals. 

Early treatment most efficient 

Their results show that cochlear injury and hearing loss in rats exposed to narrow-band noise can be substantially restored by injections of ADAC after noise exposure. Early treatment starting six hours after noise exposure was the most effective and provided greater recovery than late treatment starting 24 hours after noise exposure. The most sustainable treatment strategy was the one involving multiple injections of ADAC for five days after noise exposure. This therapy significantly attenuated noise-induced hearing loss and improved sensory hair cell survival.

The work of Dr. Srdjan Vlajkovic and his research team from The University of Auckland is published in a special edition of Springer's journal Purinergic Signalling, focusing on the inner ear.

Source: www.sciensedaily.com, Purinergic Signalling, 2010; DOI: 10.1007/s11302-010-9188-5