Abstract
Hearing loss (HL) is one of the most common causes of disability, affecting 360 million people according to the World Health Organization (WHO). HL is most frequently of sensorineural origin, being caused by the irreversible loss of hair cells and/or spiral ganglion neurons. The etiology of sensorineural HL (SNHL) is multifactorial, with genetic and environmental factors such as noise, ototoxic substances and aging playing a role. The nutritional status is central in aging disability, but the interplay between nutrition and SNHL has only recently gained attention. Dietary supplementation could therefore constitute the first step for the prevention and potential repair of hearing damage before it reaches irreversibility. In this context, different epidemiological studies have shown correlations among the nutritional condition, increased total plasma homocysteine (tHcy) and SNHL. Several human genetic rare diseases are also associated with homocysteine (Hcy) metabolism and SNHL confirming this potential link. Accordingly, rodent experimental models have provided the molecular basis to understand the observed effects. Thus, increased tHcy levels and vitamin deficiencies, such as folic acid (FA), have been linked with SNHL, whereas long-term dietary supplementation with omega-3 fatty acids improved Hcy metabolism, cell survival and hearing acuity. Furthermore, pharmacological supplementations with the anti-oxidant fumaric acid that targets Hcy metabolism also improved SNHL. Overall these results strongly suggest that cochlear Hcy metabolism is a key player in the onset and progression of SNHL, opening the way for the design of prospective nutritional therapies.
Highlights
Hearing loss (HL) is one of the most common causes of disability, affecting 360 million people according to the World Health Organization (WHO)
Pharmacological supplementations with the anti-oxidant fumaric acid that targets Hcy metabolism improved sensorineural HL (SNHL). Overall these results strongly suggest that cochlear Hcy metabolism is a key player in the onset and progression of SNHL, opening the way for the design of prospective nutritional therapies
A recent study focused on analyzing the effects of long-term administration of a polyunsaturated fatty acid (PUFA)-rich diet on cochlear Hcy metabolism showed limited SNHL prevention with no changes in serum folate levels or total plasma homocysteine (tHcy) (Martínez-Vega et al, 2015b; Figure 2)
Summary
According to the World Health Organization (2015), moderate-to-profound Hearing loss (HL) affects 360 million people worldwide. Its incidence varies in each population segment, affecting already ∼10% of children and increasing to 30% of the population over 65 years (Roth et al, 2011; Li-Korotky, 2012). HL has been ranked as the fifth leading cause of years lived with disability in the Global Burden of Disease Study 2013 Collaborators (2015). This impairment certainly limits the quality of life, and significantly increases the risk of dependance. The identification of factors involved in HL is key to understand the physiopathology, to improve diagnosis and to develop appropriate therapies and preventive behaviors
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