The effects of antioxidants in the senescent auditory cortex

Interplay between Nutrition and Hearing Loss: State of Art

Hearing loss has been recently ranked as the fifth leading cause of years lived with disability, ahead of many other chronic diseases such as diabetes, dementia, or chronic obstructive pulmonary disease. Moreover, according to the World Health Organization, moderate-to-profound hearing loss affects about 466 million people worldwide. Its incidence varies in each population segment, affecting approximately 10% of children and increasing to 30% of the population over 65 years. However, hearing loss receives still very limited research funding and public awareness. This sensory impairment is caused by genetic and environmental factors, and among the latter, the nutritional status has acquired relevance due its association to hearing loss detected in recent epidemiological studies. Several experimental models have proved that the onset and progression of hearing loss are closely linked to the availability of nutrients and their metabolism. Here, we have reviewed studies focused on nutrient effects on auditory function. These studies support the potential of nutritional therapy for the protection against hearing loss progression, which is especially relevant to the aging process and related quality of life.

Effects of Spirulina on the functions and redox status of auditory system in senescence-accelerated prone-8 mice

To our knowledge, the effects of Spirulina platensis water extract (SP) on hearing function have not yet been reported. This study investigated the effects of SP on the function and redox status of the auditory system. Auditory brainstem responses and redox status were compared between two groups of 3-month-old senescence-accelerated prone-8 (SAMP8) mice: the control group was fed a normal diet, and the experimental group was fed a normal diet with oral supplementation of SP for 6 weeks. Compared with the control group, the experimental group had significantly lower hearing thresholds according to auditory brainstem responses measured using click sounds and 8-kHz tone burst sound stimulation at the end of this study. The experimental group had a shorter I-III interval of auditory brainstem responses with 16-kHz tone burst stimulation than the control group that was of borderline significance. Additionally, the experimental group had significantly higher mRNA expression of the superoxide dismutase and catalase genes in the cochlea and brainstem and significantly higher mRNA expression of the glutathione peroxidase gene in the cochlea. Further, the experimental group had significantly lower malondialdehyde levels in the cochlea and brainstem than the control group. However, tumor necrosis factor-α mRNA expression was not significantly different between the control and experimental groups. SP could decrease hearing degeneration in senescence-accelerated prone-8 mice possibly by increasing superoxide dismutase, catalase, and glutathione peroxidase gene expression and decreasing damage from oxidative stress in the cochlea and brainstem.

Bog bilberry anthocyanin extract improves motor functional recovery by multifaceted effects in spinal cord injury

The aim of this study was to determine the therapeutic efficiency of bog bilberry anthocyanin extract (BBAE) treatment starting 1 d after spinal cord injury (SCI) in rats and to investigate the underlying mechanism. The BBAE contained cyanidin-3-glucoside, malvidin-3-galactoside and malvidin-3-glucoside. SCI models were induced using the weight-drop method in Sprague-Dawley rats and additionally with sham group (laminectomy only). The animals were divided into four groups: vehicle-treated group; 10 mg/kg BBAE-treated group; 20 mg/kg BBAE-treated group; sham group. BBAE-treated or vehicle-treated group was administered orally at one day after SCI and then daily for 8 weeks. Locomotor functional recovery was assessed during the 8 weeks post operation period by performing a Basso, Beattie, and Bresnahan (BBB) locomotor score test. At the end of study, the animals were killed, and 1.5 cm segments of spinal cord encompassing the injury site were removed for immunohistochemistry, histopathological and western blotting analysis. Immunohistochemistry for GFAP, aggrecan, neurocan and NeuN was used to assess the degree of astrocytic glial scar formation and neuron survival. Immunohistochemistry and western blotting analysis for TNF-α, IL-6, IL-1β was used to evaluate the anti-inflammation effect of BBAE. To evaluate its inhibition effect on the astrocytes, we performed the MTT assay and immunohistochemistry for Ki67 in vitro. Results show that the BBAE-treated animals showed significantly better locomotor functional recovery, neuron death and smaller glial scar formation after spinal cord injury in vivo. In addition, BBAE administration could inhibit astrocyte proliferation in vivo and vitro. Therefore, BBAE may be useful as a promising therapeutic agent for SCI.

Effects of tea drinking on auditory functions in aged subjects

The purpose of this study was to investigate the effects of Oolong tea drinking on the auditory functions in aged subjects. Retrospective cohort study was conducted on 265 subjects who were older than 55 years old. Tea drinking was determined from responses to a medical and food consumption questionnaires. The effects of Oolong tea drinking on pure tone thresholds (PTAs) for peripheral hearing and pitch pattern sequence (PPS) scores for central hearing were analyzed. Results showed that, before adjusting for other factors, PTAs were not significantly different between "non-tea drinkers" and "Oolong tea drinkes". But, the mean PPS score was higher in the "Oolong tea drinkers" (74.5 ± 12.7%) than in the "non-tea drinkers" (68.4 ± 13.9%). After adjusting for age, gender, waist circumference, and other variables, Oolong tea drinking (coefficient (β) ± standard error (SE) = 2.60 ± 0.67, P<0.001) was positively associated with PPS score, but not with PTAs, by multivariate linear regression analysis. In subgroup analysis for PPS score by gender, Oolong tea drinking showed a significant positive association with PPS score in males (β± SE=4.75 ± 0.95, P<0.001), but showed association of borderline significance with PPS score in females (β± SE=1.57 ± 0.94, P=0.097), with adjustment of other risk factors. In conclusion, Oolong tea drinking was associated with better central auditory function, but not with peripheral hearing thresholds, especially in male aged subjects.

Auditory research involving antioxidants

PURPOSE OF REVIEW

The role of antioxidants in the management of hearing loss has generated considerable interest over the past several years. Research efforts in this field have yielded many new insights into the molecular and cellular nature of several types of hearing impairment, including age-related, noise-induced, and drug-induced hearing loss. The objective of this paper is to highlight some of the important studies published over the past several years that have further contributed to our understanding of the mechanism of antioxidants in attenuating hearing loss.

RECENT FINDINGS

There is compelling evidence to suggest that antioxidant therapy is beneficial in attenuating, improving, or reversing the effects of several types of acquired hearing loss. Cellular and subcellular changes resulting from these types of hearing impairment are remarkably similar and seem to have a common putative mechanism of oxidative stress and damage. Recent studies have lent further credibility to the notion that antioxidant therapy can be of considerable benefit in the treatment of hearing loss. The increasing body of literature pertaining to human studies will shed further light into this fascinating area of research.

SUMMARY

This review elucidates the role of antioxidants in hearing loss and illustrates the continued evolution of research efforts in this field.

Cortical reorganization in the aging brain

Aging exerts major reorganization and remodeling at all levels of brain structure and function. Studies in aged animals and in human elderly individuals demonstrate that sensorimotor cortical representational maps undergo significant alterations. Because cortical reorganization is paralleled by a decline in perceptual and behavioral performance, this type of cortical remodeling differs from the plastic reorganization observed during learning processes in young individuals where map changes are associated with a gain in performance. It is now clear that brain plasticity is operational into old age; therefore, protocols for interventions such as training, exercising, practicing, and stimulation, which make use of neuroplasticity principles, are effective to ameliorate some forms of cortical and behavioral age-related changes, indicating that aging effects are not irreversible but treatable. However, old individuals cannot be rejuvenated, but restoration of function is possible through the emergence of new processing strategies. This implies that cortical reorganization in the aging brain occurs twice: during aging, and during treatment of age-related changes.