The new research is finding that hearing loss caused by certain antibiotics is actually because of the inflammation associated with the body’s reaction to infection. Inflammation causes the ion channels in the sensory hair cells on the inner ear to become permeable to antibiotics. This action also has the effect of increasing the cells’ sensitivity to the toxic effects of certain medicines. The antibiotics, known as aminoglycosides, are designed to act on a wide range of bacteria, making them useful for treating newborns with life-threatening infections. Unfortunately, these newborns have hearing loss rates six times higher than healthy newborns.
The research team tested the effects of gentamicin on mice. One protein, known as TRPV1, is involved in ion channels and enabling the drug’s entry into the hair cells. The mice involved in the study were without working TRPV1. This breeding spared the mice from the hearing loss caused by the antibiotic. The researchers observed loss-of-function mutations in TRPV1 that are dominant-negative mutations. These mutations protect the cochlea from inflammation-enhanced drug-induced hearing loss.
How do aminoglycosides cause hearing loss? It begins when a bacterial infection causes inflammation in the inner ear or other parts of the body. When inflammation is present, the number of antibiotics that are absorbed by the internal components of the ear increases. When too many of these toxins absorb into the inner parts of the ear, the sensory cells that detect sound and motion die. The majority of individuals who lose their hearing due to aminoglycosides are infants who receive the antibiotic due to life-threatening infections. Those infants in neonatal units are of particular concern. Although aminoglycosides have been in use for over 50 years, they are widely available, inexpensive, do not require refrigeration, and are incredibly effective at saving lives.
The research team feels that, if possible, doctors should use antibiotics that don’t increase the risk of a hearing loss in patients with body-wide infection. If aminoglycosides are the only option, healthcare professionals can be aware of those who most likely need post-treatment auditory rehabilitation much earlier. This information can help to inform patients with a drug-induced hearing loss of how this type of hearing loss happened to them. Most importantly, the investigators now know that those with severe infections are now likely much more susceptible to aminoglycoside-induced hearing loss.
The reason for the research is to find new pharmacotherapeutics that prevent drug, noise, and age-related hearing loss. The study gives the team the confidence that otoprotective medications can play a significant role in avoiding hearing loss due to antibiotics. The discoveries will help to create specific druggable targets to improve otoprotectants and to prevent hearing loss. There is also a new form of aminoglycoside currently under development, which is particularly exciting news. The developers hope that the new antibiotic will deliver the same life-saving benefits without the resulting hearing loss.