A team of Argentine researchers has verified that presbycusis or hearing loss associated with aging is related to a reduction in cholesterol in the inner ear. The study they have carried out has found that phytosterol supplements replaced the lost cholesterol activity and, in this way, they were able to prevent this hearing defect in mice.
Sensory cells in the inner ear are known as outer hair cells (OTCs) and are responsible for amplifying sounds by changing their length, but these cells lose their ability to stretch in response to sound as we age, leading to related hearing loss with the age.
Because cholesterol is a key factor in the stretch response, and brain cholesterol has recently been shown to also drop over the years, the researchers hypothesized that hearing loss might be related to hearing loss. decreased cholesterol in SCCs and did tests in mice to test their hypothesis.
Phytosterols improved the function of ear hair cells
The researchers, led by María Eugenia Gómez-Casati, from the Institute of Pharmacology, Faculty of Medicine, University of Buenos Aires-CONICET, Mauricio Martín, from the Mercedes and Martín Ferreyra Institute of Medical Research, (INIMEC-CONICET-UNC) from the University Nacional de Córdoba, in Argentina, began by measuring the amount of CYP46A1 in the SCCs of the inner ear because this enzyme helps break down and recycle cholesterol.
“Our findings provide the first evidence supporting phytosterol supplementation as a possible approach for the prevention or treatment of hearing loss.”
They found more CYP46A1 in the inner ear of the older mice than in the younger ones, and as a result, less cholesterol. They then demonstrated cause and effect by inducing hearing loss in young mice – indicated by abnormal inner ear cell production – through overactivation of CYP46A1 with a drug. And finally, they checked whether the increase in cholesterol in the brain could counteract the action of the drug.
Because cholesterol itself cannot enter the brain from the blood, the researchers used cholesterol-like plant compounds called phytosterols that do have that ability, and found that young mice given both the CYP46A1-activating drug and three weeks of phytosterols in the diet, experienced an improvement in CCE function.
Phytosterols can be found in many over-the-counter supplements, so they could be a useful resource in combating age-related hearing loss. Before this, however, its effects on hearing loss will need to be tested directly in older mouse models, as well as in humans, to allow more definitive conclusions to be drawn.
The authors have explained: “In the present work we show that: 1) aging triggers the loss of cholesterol from the sensory cells of the inner ear, 2) a widely used retroviral treatment for HIV/AIDS patients reproduces the cholesterol loss observed in elderly people and leads to impaired outer hair cell function and 3) found that these defects can be partly reversed by phytosterol supplementation.”
“Our findings are very promising because they provide the first proof-of-principle supporting phytosterol supplementation as a possible approach for the prevention or treatment of hearing loss,” the researchers state. The results of the study have been published in PLOS Biology.
