A team of scientists from the University of Miami and Stanford University has studied the genetic basis of sensorineural hearing loss—hearing loss due to damage to the sound-perceiving organ (such as the inner ear or auditory nerve). This type of hearing loss is usually inherited and manifests in early childhood. In most cases, there is no medical cure for such patients. However, an article published in the Journal of Clinical Investigation offers a potential therapeutic target. The researchers demonstrated that one of the causes of hereditary sensorineural hearing loss may be a mutation in the *CPD* gene, which is responsible for the synthesis of carboxypeptidase D. The CPD protein maintains the concentration of arginine in hair cells—the receptors in the ear that convert mechanical fluid vibrations in the cochlea into electrical impulses. Specifically, arginine is necessary for the creation of nerve signaling substances: nitric oxide and cyclic guanosine monophosphate (cGMP), which help hair cells properly respond to sound. The discovery is that hearing loss triggered by the incorrect function of the *CPD* gene may be reversible. Experiments on mice and flies in which the *CPD* gene was intentionally deactivated showed that: taking arginine supplements prevents the death of hair cells, and the substance sildenafil increases the concentration of the signaling molecule cGMP. Sildenafil is the active ingredient in medications used to enhance potency. It inhibits the enzyme PDE-5 (phosphodiesterase-5), causing smooth muscles to relax and blood vessels to dilate—this ensures an erection. However, the PDE-5 enzyme also breaks down the signaling molecule cGMP, which is important for hearing. If it is blocked, the level of cGMP will remain high, and the hair cells will not be destroyed. This can be considered a favorable side effect of Viagra. Thus, it is possible that in the future, potency drugs may become a new method for treating hereditary hearing loss. Important. These are only laboratory findings and studies on mice. How arginine dietary supplements and potency drugs affect hearing in humans is unknown.
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