Stem cell research is progressing at a rapid pace, with new breakthroughs occurring on a regular basis.  There are dozens of stem cell clinical trials currently underway, which hope to develop new treatments for medical conditions including heart disease, blindness, Parkinson’s disease, Alzheimer’s disease and much more.

Stem cells may also be useful for the treatment of hearing loss and deafness. This article will explain how hearing loss occurs and how new stem cell therapies may be used to treat hearing loss.

About Hearing Loss

Hearing loss is very common in the developed world. In the United Kingdom, one in six people have some form of hearing impairment and 800,000 people have severe or profound deafness (Actiononhearingloss.org.uk, 2015).  In the United States, an estimated 17% of people have some form of hearing loss (Hsci.harvard.edu, 2015).

Hearing loss is particularly widespread amongst older people, with 70% of people over 70 years of age and 40% of people over 50 years of age having some form of hearing loss in the United Kingdom (Actiononhearingloss.org.uk, 2015).

There are only a few statistics available for the United Arab Emirates. However, a recent report estimates that 1 in 25 people are affected by hearing loss in the Middle East and 87% of medical specialists suggest that hearing loss is a severe health issue for people in the region (Health Magazine, 2015).

To understand how researchers hope to use stem cells for hearing loss, it is important to understand how hearing loss occurs. There are two main forms of hearing loss, Sensorineural Hearing Loss (SNHL) and Conductive hearing loss.

Sensorineural Hearing Loss (SNHL)

The ear’s cochlea contains tiny hair-like nerve endings called inner hair cells (IHC) and  outer hair cells (OHC). They transduce sound into electrical signals that are sent to the brain. SNHL occurs when those nerve endings have been damaged or have died. SNHL can also occur when the neural pathways between the ear and the brain (called the spiral ganglion neurones) have been damaged. SNHL is considered to be a permanent form of hearing loss because once the nerves in the ear are damaged or killed, they will not regrow.

Conductive Hearing Loss

This form of hearing loss occurs when there is some kind of blockage affecting the ear canal, middle ear or eardrum that prevents sound from traveling through to the cochlea. This form of hearing loss can often be treated with surgery or medication.

Hearing loss is caused by a number of  different diseases, injuries and congenital abnormalities. The leading causes of hearing loss are:

• Age-related hearing loss (Presbycusis) – Can be caused by changes to the middle ear, changes to the nerves between the ear and brain, certain medical conditions or certain medications. It is a form of SNHL.
• Noise-related hearing loss – From continuous or intermittent exposure to very loud noises that damage the ear.  Also considered a form of SNHL.
• Childhood infections – Certain childhood infections including Meniere’s disease, meningitis, mumps, measles and scarlet fever can cause SNHL.
• Blockages in the Ear – Congenital abnormalities, tumours, head trauma or a foreign body within the ear can cause conductive hearing loss.

Using Stem Cells for Hearing Loss

A number of universities, research foundations and hospitals have begun initiatives to find stem cell treatments for hearing loss.  They include The Stanford Initiative to Cure Hearing Loss and The Harvard Stem Cell Institute, who are leaders in the field of stem cell research.

Much of the research undertaken so far focusses on using stem cells to regrow the nerve endings within the ear. Scientists are also interested in repairing the spiral ganglion neurones that carry electrical signals between the ear and the brain.

Multipotent stem cells are ideal for regenerating the nerves in the ear because they are capable of differentiating into many types of cells. Umbilical cord blood is a rich source of these multipotent stem cells and frequently used by researchers.

Scientists already understand which multipotent stem cells can develop into ear nerve endings from experiments on stem cells in petri dishes (Hsci.harvard.edu, 2015). Researchers have also discovered ways to create stem-cell-derived auditory neurones that can form new connections with damaged hair cells in the ear. The difficult part is translating the processes from a petri dish to live test subjects.

Harvard researchers have already taken some huge steps towards replicating the results in animal testing.  In a 2014 animal trial, Harvard researchers successfully regenerated the nerve endings within the cochlea (Hsci.harvard.edu, 2015). The mice had a form of sensorineural hearing loss, which is the most type of hearing loss in humans. The mice’s nerve endings began to regrow and they regained some of their hearing after the stem cell transplant.

Researchers at Stanford are also trying to develop a stem cell treatment for congenital hearing loss.  They have also made some important breakthroughs in the understanding of how the ear’s hair cells work in mammals (Morris, 2015).

The Florida Hospital for Children has announced a study which will examine the safety of stem cell transfusions for children with hearing loss. The phase I safety study will look at the use of autologous stem cells from umbilical cord blood that has been transfused into children with SNHL (Clinicaltrials.gov, 2015). The trial hopes to demonstrate that the treatment is effective while remaining safe.

If research continues to demonstrate positive results, a cure for the most common forms of hearing loss may only be a few years away.  It is a very exciting time in the field of stem cell research and these breakthroughs give a great deal of hope to people with a hearing impairment.

Sources

Actiononhearingloss.org.uk,. (2015). Statistics – Action On Hearing Loss: RNID. Retrieved 9 October 2015, from http://www.actiononhearingloss.org.uk/your-hearing/about-deafness-and-hearing-loss/statistics.aspx 

Hsci.harvard.edu,. (2015). Hearing Loss. Retrieved 9 October 2015, from http://hsci.harvard.edu/hearing-loss-0 

Morris, K. (2015). 2014 Research Report | Stanford Initiative to Cure Hearing Loss. Hearinglosscure.stanford.edu. Retrieved 10 October 2015, from https://hearinglosscure.stanford.edu/2014/12/2014-research-report/ 

Health Magazine,. (2015). MED-EL ANNOUNCES RESULTS OF THE ‘FIRST SPECIAL REPORT ON HEARING LOSS IN THE MIDDLE EAST’. Retrieved 9 October 2015, from http://www.healthmagazine.ae/press_release/med-el-announces-results-of-the-first-special-report-on-hearing-loss-in-the-middle-east/ 

Clinicaltrials.gov,. (2015). Safety of Autologous Stem Cell Infusion for Children With Acquired Hearing Loss – Full Text View – ClinicalTrials.gov. Retrieved 10 October 2015, from https://clinicaltrials.gov/ct2/show/NCT02038972?term=Florida+Hospital+stem+cells&rank=1 

Hsci.harvard.edu,. (2015). Harvard researchers regenerate sound-sensing cells of mice with hearing damage. Retrieved 10 October 2015, from http://hsci.harvard.edu/news/harvard-researchers-regenerate-sound-sensing-cells-mice-hearing-damage

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