Serum homocysteine and folate concentrations are associated with prevalent age-related hearing loss

Relationship Between Serum Brain-Derived Neurotrophic Factor and Neurotrophin-3 Levels and Hearing Thresholds in Patients With Age-Related Hearing Loss

BACKGROUND

Age-related hearing loss (ARHL) is a general term used to describe the sensorineural type of hearing loss occurring in both ears in older adults. Neurotrophins are the most promising candidates for supporting the auditory nerve by increasing neuronal survival. This study aimed to help elucidate the pathophysiology of ARHL by determining whether any relationship exists between brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) levels in serum samples from patients diagnosed with ARHL.

MATERIALS AND METHOD

Seventy-seven individuals, a study group of 41 patients diagnosed with ARHL, and a control group of 36 participants without hearing loss were evaluated. Serum samples were collected and used to measure serum BDNF and NT-3 levels with the new Nepenthe enzyme-linked immunosorbent assay method.

RESULTS

Median pure-tone average results in the 2000, 4000, and 6000 Hz ranges were 52.5 (44.3-67.3) dB HL in the ARHL group and 13.5 (11.1-17.1) dB HL in the control group. The difference was statistically significant (p = .001). Although NT-3 and BDNF levels were both lower in ARHL patients than in participants without hearing loss, only the BDNF levels were significantly (p = .002) lower. Mean left and right ear word recognition scores were also lower in ARHL patients than in control groups. The ARHL group was further divided into two subgroups based on word recognition scores to evaluate significant differences in BDNF and NT-3 levels. No statistically significant difference was observed in BDNF and NT-3 levels between these subgroups. However, there was a significant difference in word recognition scores.

CONCLUSIONS

Low BDNF levels in the ARHL group suggest that BDNF may play a role in the pathogenesis of ARHL. Patients with low (ARHL1) and high (ARHL2) word recognition scores were compared for the first time in the literature in terms of BDNF and NT-3 levels. However, the results were not statistically significant. This article is a preliminary study and was written to provide guidance for our next comprehensive project.

The effect of vitamin B12 on idiopathic tinnitus

INTRODUCTION

Tinnitus is one of the most important challenges in the field of ear, nose and throat diseases. The aim of this study was to evaluate the effect of vitamin B12 on idiopathic tinnitus.

MATERIAL AND METHODS

In this double-blind clinical trial study, 140 patients with idiopathic tinnitus were divided into two groups, the group receiving vitamin B12 and the group receiving placebo. The first group received vitamin B12 for a month and the other group received placebo. All patients filled a THI questionnaire before the participation, one month and three months after the participation. VAS evaluation questionnaires were also filled for the patients before the participation, one month and three months after the participation. The effect of vitamin B12 on tinnitus was also assessed according to hearing loss status. The two groups were also compared regarding the side effects.

RESULTS

There was no significant differences between two groups regarding age (p.value = 0.523), gender (females (p.value = 0.810) and males (p.value = 0.789), and hearing loss status (p value = 0.651). According to VAS score, there was no significant statistical differences in tinnitus severity in each group (B12 group, p.value = 0.851 and placebo group, p.value = 0.386). There was no significant statistical differences in tinnitus severity based on VAS score between two groups before the participation (p.value = 0.560), one month (p.value = 0.485) and three months (p.value = 0.254) after the participation. According to THI criterion, there was no significant statistical differences in tinnitus severity in each group (B12 group, p.value = 0.259 and placebo group, p.value = 0.521). There was no significant statistical differences in tinnitus severity based on THI score between two groups before the participation (p.value = 0.651), one month (p.value = 0.125) and three months (p.value = 0.089) after the participation. None of the patients of the two groups had any noticeable side effects. The mean of VAS and THI also had no statistically significant difference before and after the intervention in term of hearing loss status (p.value>0.05). These results were not significantly different between the two groups in term of hearing loss status (p value>0.05).

CONCLUSION

The result of this study indicated that vitamin B12 has no distinctive effect on reducing tinnitus severity.

The Role of Fibrinogen, Homocysteine and Metabolic Syndrome's Alterations in Sudden Sensorineural Hearing Loss (SSHL): A Narrative Review

Fibrinogen and homocysteine (HCY) are molecules known to play a role in vascular homeostasis, and their blood levels are often elevated in patients with metabolic syndrome. Recent evidence suggests that sudden sensorineural hearing loss (SSHL) may have a vascular origin. This has led many authors to advocate that fibrinogen, homocysteine, and metabolic syndrome (MetS) may play a direct role in SSHL. The aim of this brief review is to examine the role and influence of these molecules and MetS on the mechanisms of SSHL. Elevated fibrinogen levels have been associated with a worse prognosis in SSHL, possibly due to increased blood viscosity and decreased blood flow. Similarly, HCY has been associated with vascular damage, particularly in hyperhomocysteinemia, although the exact association with SSHL remains controversial. MetS has been demonstrated to function both as a causative factor and as a contributor to poorer recovery in cases of SSHL. However, although some studies suggest a possible role for these biomarkers and MetS in the prognosis and treatment of SSHL, specific therapeutic and preventive strategies based solely on these factors have yet to be developed. Given their potential role in prognosis and treatment and the global epidemic of metabolic syndrome, this issue needs to be analyzed comprehensively. Thus, further quality studies need to be conducted, even though it is difficult to determine the actual impact of MetS on the development of SSHL, as it is a multifactorial disease affecting multiple organs.

Intrinsic Capacity Declines with Elevated Homocysteine in Community-Dwelling Chinese Older Adults

Purpose

Intrinsic capacity (IC) reflects the overall health status of older adults and has great public health significance. But few studies described the related biomarkers for IC. The aim of this study was to investigate the association between homocysteine (Hcy) and IC in older adults.

Participants and Methods

This cross-sectional study included 1927 community-dwelling Chinese older adults aged 60–98 years from May 2020 to December 2020. Data were collected through interviews, physical examinations, and laboratory tests. IC involved five domains of cognition, locomotion, sensory, vitality, and psychology evaluated by the Mini-cog scale, 4-m walk test, self-reported visual and hearing conditions, MNA-SF scale, and GDS-4 scale, respectively. The score of each domain dichotomized as 0 (normal) and 1 (impaired) was added together to an IC total score. Low IC was defined as a score of 3–5, and high IC as 0–2. Hcy was measured by a two-reagent enzymatic assay. A restricted cubic spline regression model was used to explore the non-linear relationship between Hcy and low IC.

Results

Hcy was higher in the low IC group than in the high IC group. Restricted cubic spline analysis revealed a J-shaped nonlinear association between Hcy and low IC. The risk of IC decline was slowly decreased until 8.53 µmol/L of Hcy (OR=0.753, 95% CI=0.520–1.091, P=0.132), and increased with elevations of per 5 µmol/L Hcy afterwards (OR=1.176, 95% CI=1.059–1.327, P=0.005). Among the five domains of IC, Hcy had ORs of 1.116 (1.009–1.247) for cognition impairment, 1.167 (1.055–1.305) for vitality, and 1.160 (1.034–1.303) for psychology per 5 µmol/L increase in Hcy above the change point. Additional sensitivity analysis also demonstrated the nonlinear association between Hcy and low IC.

Conclusion

Hcy had a J-shaped association with low IC. Higher Hcy (Hcy ≥8.53µmol/L) might provide clinical implications for early identifying the risk of low IC.

The Inverted-U Relationship Between Dietary Inflammatory Potential and Hearing Loss Among Adults Aged 20 Years and Over in the United States: A Cross-Sectional Study

Purpose

The purpose of this study was to examine the relationship between dietary inflammatory index and objective hearing loss (HL).

Materials and Methods

A cross-sectional analysis of a nationally representative sample of participants was performed based on data in National Health and Nutrition Examination Survey (NHANES) (2009-2016). HL was defined as pure tone averages >25 dB at 500, 1000, and 2000 Hz (low frequency); 3000, 4000, 6000, and 8000 Hz (high frequency) in either ear. The energy-adjusted dietary inflammatory index (E-DII) score was calculated for each participant based on two 24-h dietary recalls to assess diet-associated inflammation. Multivariable logistic regression was used to examine the linear relationship between HL and E-DII score or E-DII quartiles. Restricted cubic spline was applied to identify any non-linear associations of the E-DII score with hearing loss. Subgroup analyses were performed by age and gender to explore the moderating roles of these factors. Akaike's Information Criterion (AIC) values were used to select the better-fitted model among linear and non-linear models.

Results

An inverted-U shaped relationship with low-frequency hearing loss (LFHL) was identified for the E-DII score (P-nonlinear =0.023) after adjustment for potential confounders. But significant linear or nonlinear association between E-DII score and high-frequency hearing loss (HFHL) was not found.

Conclusion

E-DII score had inverted-U relationship with LFHL. Both pro-inflammatory diet and anti-inflammatory diet seemed to be associated with a decreased risk of LFHL compared to diet that was neither pro-inflammatory diet nor anti-inflammatory diet.

Relationship Between Diet, Tinnitus, and Hearing Difficulties

OBJECTIVES

Diet may affect susceptibility of the inner ear to noise and age-related effects that lead to tinnitus and hearing loss. This study used complementary single nutrient and dietary pattern analysis based on statistical grouping of usual dietary intake in a cross-sectional analysis of tinnitus and hearing difficulties in a large population study sample.

DESIGN

The research was conducted using the UK Biobank resource. Tinnitus was based on report of ringing or buzzing in one or both ears that lasts more than five minutes at a time and is currently experienced at least some of the time. Identification of a hearing problem was based on self-reported difficulties with hearing. Usual dietary intake and dietary patterns (involving statistical grouping of intake to account for how foods are combined in real-life diets) were estimated based on between two and five administrations of the Oxford Web-Q 24-hour dietary recall questionnaire over the course of a year for 34,576 UK adult participants aged 40 to 69.

RESULTS

In a multivariate model, higher intake of vitamin B12 was associated with reduced odds of tinnitus, while higher intakes of calcium, iron, and fat were associated with increased odds (B12, odds ratio [OR] 0.85, 95% confidence interval [CI] 0.75 to 0.97; Calcium, OR 1.20, 95% CI 1.08 to 1.34; Iron, OR 1.20, 95% CI 1.05 to 1.37; Fat, OR 1.33, 95% CI 1.09 to 1.62, respectively, for quintile 5 versus quintile 1). A dietary pattern characterised by high protein intake was associated with reduced odds of tinnitus (OR 0.90, 95% CI 0.82 to 0.99 for quintile 5 versus quintile 1). Higher vitamin D intake was associated with reduced odds of hearing difficulties (OR 0.90, 95% CI 0.81 to 1.00 for quintile 5 versus quintile 1), as were dietary patterns high in fruit and vegetables and meat and low in fat (Prudent diet: OR 0.89, 95% CI 0.83 to 0.96; High protein: OR 0.88, 95% CI 0.82 to 0.95; High fat: OR 1.16, 95% CI 1.08 to 1.24, respectively, for quintile 5 versus quintile 1).

CONCLUSIONS

There were associations between both single nutrients and dietary patterns with tinnitus and hearing difficulties. Although the size of the associations was small, universal exposure for dietary factors indicates that there may be a substantial impact of diet on levels of tinnitus and hearing difficulties in the population. This study showed that dietary factors might be important for hearing health.

Hearing status in vitamin B12-deficient children

AIM

The aim of this study is to investigate the effects of vitamin B12 deficiency on hearing in school-aged children by pure-tone audiometry.

METHODS

Forty-three vitamin B12-deficient children and 37 age-matched control subjects were enrolled in the study. Tympanometric evaluations and pure-tone audiometry including high frequencies were performed on the subjects. The results were compared between the two groups.

RESULTS

Both right and left ear pure-tone hearing thresholds (PTHTs) at 0.25-4 kHz, and four-frequency pure-tone average values were significantly better in the control group compared with the patient group (P < 0.05). However, PTHTs at 8-16 kHz were not different between the two groups (P > 0.05). Vitamin B12 level also did not show any significant correlation with the PTHTs at 0.25-16 kHz (P > 0.05).

CONCLUSION

This study indicates that vitamin B12 deficiency may contribute to hearing impairment at low frequencies as a possible aetiological factor in children.

Low vitamin B12 level and vitamin D level adversely affect on cochlear health in women

The aim of this study is to examine the association between low serum vitamin B₁₂ levels and low serum vitamin D levels and cochlear health in women. A prospective case-control study was carried out in the Department of Otolaryngology, Malatya Training and Research Hospital between 2017-2018. Thirty (30) patients with vitamin B₁₂ deficiency (a mean age of 32.5 ± 1.7 years(y) women); 30 patients with vitamin D deficiency (a mean age of 32.3 ± 1.58 y women) and 30 controls (a mean age of 27.8 ± 1.48 y women) were recruited. The study participants have no evidence of symptomatic hearing loss. Transiently evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) of the study participants were recorded. A comparative analysis of the parameters revealed that results at TEOAE 1,2,3,4 kHz (p = 0.013, p = 0.002, p = 0.001, p = 0.001, respectively) and at DPOAE 1, 2, 6 kHz (p < 0.001, p < 0.001, p = 0.002, respectively) were somewhat lower in patients with vitamin B₁₂ deficient group when compared with the controls. Moreover, TEOAE 3,4 kHz (p = 0.005, p = 0.013 respectively) and DPOAE 1,2,6 kHz (p = 0.005, p = 0.01, p = 0.031, respectively) were lower in the vitamin D deficiency group compared with the controls. There was a significant association between both vitamin B₁₂ deficiency and vitamin D deficiency and cochlear health. Patients with vitamin B₁₂ and vitamin D deficiency should be evaluated for cochlear function.

Advances in understanding of presbycusis

The pathophysiology of age-related hearing loss (ARHL), or presbycusis, involves a complex interplay between environmental and genetic factors. The fundamental biomolecular mechanisms of ARHL have been well described, including the roles of membrane transport, reactive oxygen species, cochlear synaptopathy, vascular insults, hormones, and microRNA, to name a few. The genetic basis underlying these mechanisms remains under-investigated and poorly understood. The emergence of genome-wide association studies has allowed for the identification of specific groups of genes involved in ARHL. This review highlights recent advances in understanding of the pathogenesis of ARHL, the genetic basis underlying these processes and suggests future directions for research and potential therapeutic avenues.

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.

Mammalian Sulfur Amino Acid Metabolism: A Nexus Between Redox Regulation, Nutrition, Epigenetics, and Detoxification

SIGNIFICANCE

Transsulfuration allows conversion of methionine into cysteine using homocysteine (Hcy) as an intermediate. This pathway produces S-adenosylmethionine (AdoMet), a key metabolite for cell function, and provides 50% of the cysteine needed for hepatic glutathione synthesis. The route requires the intake of essential nutrients (e.g., methionine and vitamins) and is regulated by their availability. Transsulfuration presents multiple interconnections with epigenetics, adenosine triphosphate (ATP), and glutathione synthesis, polyol and pentose phosphate pathways, and detoxification that rely mostly in the exchange of substrates or products. Major hepatic diseases, rare diseases, and sensorineural disorders, among others that concur with oxidative stress, present impaired transsulfuration. Recent Advances: In contrast to the classical view, a nuclear branch of the pathway, potentiated under oxidative stress, is emerging. Several transsulfuration proteins regulate gene expression, suggesting moonlighting activities. In addition, abnormalities in Hcy metabolism link nutrition and hearing loss.

CRITICAL ISSUES

Knowledge about the crossregulation between pathways is mostly limited to the hepatic availability/removal of substrates and inhibitors. However, advances regarding protein-protein interactions involving oncogenes, identification of several post-translational modifications (PTMs), and putative moonlighting activities expand the potential impact of transsulfuration beyond methylations and Hcy.

FUTURE DIRECTIONS

Increasing the knowledge on transsulfuration outside the liver, understanding the protein-protein interaction networks involving these enzymes, the functional role of their PTMs, or the mechanisms controlling their nucleocytoplasmic shuttling may provide further insights into the pathophysiological implications of this pathway, allowing design of new therapeutic interventions. Antioxid. Redox Signal. 29, 408-452.

Erythrocyte folate, serum vitamin B12, and hearing loss in the 2003-2004 National Health And Nutrition Examination Survey (NHANES)

BACKGROUND/OBJECTIVES

Studies based on food frequency questionnaires suggest that folate and vitamin B12 intake could protect against hearing loss. We investigated whether erythrocyte folate and serum vitamin B12 levels are independently associated with hearing loss in humans.

SUBJECTS/METHODS

Participants in the 2003-2004 US National Health and Nutrition Examination Survey who had data on hearing, folate, and vitamin B12 levels were included. Pure-tone average (PTA) at 0.5, 1.0, 2.0, and 4.0 kHz was computed for each ear. We used weighted logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the relation between quartiles of folate and vitamin B12, and hearing loss (present if PTA > 25 dB in either ear and absent if PTA ≤ 25 dB in both ears).

RESULTS

Participants (n = 1149) were 20-69 (mean 42) years old and 16.4% had hearing loss in at least one ear. Our data suggest a U-shaped relationship between folate and hearing loss. Compared to the 1st quartile, the ORs (95% CIs) for hearing loss were 0.87 (0.49-1.53), 0.70 (0.49-1.00), and 1.08 (0.61-1.94) for the 2nd, 3rd, and 4th quartile of erythrocyte folate in analyses adjusted for age, sex, vitamin B12, smoking, alcohol use, body mass index, race/ethnicity, exposure to noise, income, and education. Although we observed inverse associations between vitamin B12 and hearing loss, the associations were not statistically significant (P > 0.05).

CONCLUSIONS

Our data show a U-shaped relationship between erythrocyte folate levels and hearing loss, suggesting a need to evaluate whether optimizing blood folate levels could prevent hearing loss.

Carotenoids, vitamin A, vitamin C, vitamin E, and folate and risk of self-reported hearing loss in women

BACKGROUND

Higher intake of certain vitamins may protect against cochlear damage from vascular compromise and oxidative stress, thereby reducing risk of acquired hearing loss, but data are limited.

OBJECTIVE

We prospectively examined the relation between carotenoids, vitamin A, vitamin C, vitamin E, and folate intake and risk of self-reported hearing loss in women.

DESIGN

This prospective cohort study followed 65,521 women in the Nurses' Health Study II from 1991 to 2009. Baseline and updated information obtained from validated biennial questionnaires was used in Cox proportional hazards regression models to examine independent associations between nutrient intake and self-reported hearing loss.

RESULTS

After 1,084,598 person-years of follow-up, 12,789 cases of incident hearing loss were reported. After multivariable adjustment, we observed modest but statistically significant inverse associations between higher intake of β-carotene and β-cryptoxanthin and risk of hearing loss. In comparison with women in the lowest quintile of intake, the multivariable-adjusted RR of hearing loss among women in the highest quintile was 0.88 (95% CI: 0.81, 0.94; P-trend < 0.001) for β-carotene and 0.90 (95% CI: 0.84, 0.96; P-trend < 0.001) for β-cryptoxanthin. In comparison with women with folate intake 200-399 μg/d, very low folate intake (<200 μg/d) was associated with higher risk (RR: 1.19; 95% CI: 1.01, 1.41), and higher intake tended to be associated with lower risk (P-trend = 0.04). No significant associations were observed for intakes of other carotenoids or vitamin A. Higher vitamin C intake was associated with higher risk; in comparison with women with intake <75 mg/d, the RR among women with vitamin C intake ≥1000 mg/d (mainly supplemental) was 1.22 (95% CI: 1.06, 1.42; P-trend = 0.02). There was no significant trend between intake of vitamin E intake and risk.

CONCLUSION

Higher intakes of β-carotene, β-cryptoxanthin, and folate, whether total or from diet, are associated with lower risk of hearing loss, whereas higher vitamin C intake is associated with higher risk.

MMP-9 gene ablation mitigates hyperhomocystenemia-induced cognition and hearing dysfunction

Hyperhomocysteinemia (HHcy) is associated with cognitive decline and hearing loss due to vascular dysfunction. Although we have shown that HHcy-induced increased expression of matrix metalloproteinase-9 (MMP-9) is associated with cochlear pathology in cystathionine-β-synthase heterozygous (CBS(+/-)) mice, it is still unclear whether MMP-9 contributes to functional deficit in cognition and hearing. Therefore, we hypothesize that HHcy-induced MMP-9 activation causes vascular, cerebral and cochlear remodeling resulting in diminished cognition and hearing. Wildtype (WT), CBS(+/-), MMP-9(-/-) and CBS(+/-)/MMP-9(-/-) double knock-out (DKO) mice were genotyped and used. Doppler flowmetry of internal carotid artery (ICA) was performed for peak systolic velocity [PSV], pulsatility index [PI] and resistive index [RI]. Cognitive functions were assessed by Novel Object Recognition Test (NORT) and for cochlear function Auditory brainstem response (ABR) was elicited. Peak systolic velocity, pulsatility and resistive indices of ICA were decreased in CBS(+/-) mice, indicating reduced perfusion. ABR threshold was increased and maximum ABR amplitude and NORT indices (recognition, discrimination) were decreased in CBS(+/-) mice compared to WT and MMP-9(-/-). All these parameters were attenuated in DKO mice suggesting a significant role of MMP-9 in HHcy-induced vascular, neural and cochlear pathophysiology. Regression analysis of PSV with ABR and cognitive parameters revealed significant correlation (0.44-0.58). For the first time, MMP-9 has been correlated directly to functional deficits of brain and cochlea, and found to have a significant role. Our data suggests a dual pathology of HHcy occurring due to a decrease in blood supply (vasculo-neural and vasculo-cochlear) and direct tissue remodeling.

Low-fat and low-protein diets are associated with hearing discomfort among the elderly of Korea

Research on the effect of low-fat intake on hearing is limited. This study aimed to elucidate the relationship between fat, carbohydrate and protein intake and the presence of hearing discomfort among the elderly. The Korean National Health and Nutrition Examination Survey was conducted from 2009 through to 2012. A total of 4615 participants ranging in age from 60 to 80 years underwent a pure-tone audiometric evaluation, a physical examination and a nutritional survey. The associations between the participants' hearing thresholds and their protein/fat/carbohydrate intake/total energy intake were analysed using simple and multiple regression models with complex sampling adjusted for confounding factors, such as BMI, income level, smoking status and a history of hypertension, hyperlipidaemia and diabetes. Low fat and protein intakes were associated with hearing discomfort (OR 0·82, 95 % CI 0·71, 0·96, P=0·011; OR 0·81, 95 % CI 0·67, 0·96, P=0·017, respectively). This study revealed that low fat and protein intakes are associated with hearing discomfort in the elderly Korean population.

Long-term omega-3 fatty acid supplementation prevents expression changes in cochlear homocysteine metabolism and ameliorates progressive hearing loss in C57BL/6J mice

Omega-3 polyunsaturated fatty acids (PUFAs) are essential nutrients well known for their beneficial effects, among others on cognitive development and maintenance, inflammation and oxidative stress. Previous studies have shown an inverse association between high plasma levels of PUFAs and age-related hearing loss, and the relationship between low serum folate and elevated plasma homocysteine levels and hearing loss. Therefore, we used C57BL/6J mice and long-term omega-3 supplementation to evaluate the impact on hearing by analyzing their auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) thresholds. The omega-3 group showed significantly lower ABR hearing thresholds (~25 dB sound pressure level) and higher DPOAE amplitudes in mid-high frequencies when compared to the control group. These changes did not correlate with alterations between groups in plasma homocysteine or serum folate levels as measured by high-performance liquid chromatography and a microbiological method, respectively. Aging in the control group was associated with imbalanced cytokine expression toward increased proinflammatory cytokines as determined by quantitative reverse transcriptase polymerase chain reaction; these changes were prevented by omega-3 supplementation. Genes involved in homocysteine metabolism showed decreased expression during aging of control animals, and only alterations in Bhmt and Cbs were significantly prevented by omega-3 feeding. Western blotting showed that omega-3 supplementation precluded the CBS protein increase detected in 10-month-old controls but also produced an increase in BHMT protein levels. Altogether, the results obtained suggest a long-term protective role of omega-3 supplementation on cochlear metabolism and progression of hearing loss.

Age-related hearing impairment and the triad of acquired hearing loss

Understanding underlying pathological mechanisms is prerequisite for a sensible design of protective therapies against hearing loss. The triad of age-related, noise-generated, and drug-induced hearing loss displays intriguing similarities in some cellular responses of cochlear sensory cells such as a potential involvement of reactive oxygen species (ROS) and apoptotic and necrotic cell death. On the other hand, detailed studies have revealed that molecular pathways are considerably complex and, importantly, it has become clear that pharmacological protection successful against one form of hearing loss will not necessarily protect against another. This review will summarize pathological and pathophysiological features of age-related hearing impairment (ARHI) in human and animal models and address selected aspects of the commonality (or lack thereof) of cellular responses in ARHI to drugs and noise.

Intake of specific nutrients and foods and hearing level measured 13 years later

Only a few studies have investigated the impact of nutrients and food groups on hearing level (HL) with a population-based approach. We examined the 13-year association between intake of specific nutrients and food groups and HL in a sample of French adults. A total of 1823 subjects, aged 45-60 years at baseline, participating in the Supplementation with Antioxidant Vitamins and Minerals 2 cohort were selected. Nutrient and food intake was estimated at baseline among participants who had completed at least six 24 h dietary records. HL was assessed 13 years after baseline and was defined as the pure-tone air conduction of the worse ear at the following thresholds: 0·5, 1, 2 and 4 kHz. The relationship between quartiles of energy-adjusted nutrient and food intake and HL was assessed by multivariate linear regression analyses, in men and women separately. Intakes of retinol (P-trend ¼ 0·058) and vitamin B12 (P-trend=0·068) tended to be associated with better HL in women. Intakes of meat as a whole (P-trend=0·030), red meat (P-trend=0·014) and organ meat (P-trend=0·017) were associated with better HL in women. Higher intake of seafood as a whole (P-trend=0·07) and of shellfish (P-trend=0·097) tended to be associated with better HL in men. Consumption of meat is therefore associated with a better HL in women. Further research is required to better elucidate the mechanisms behind the associations between diet and hearing.

Folic acid improves inner ear vascularization in hyperhomocysteinemic mice

More than 29 million adults in the United States have been diagnosed with hearing loss. Interestingly, elevated homocysteine (Hcy) levels, known as hyperhomocysteinemia (HHcy), are also associated with impaired hearing. However, the associated mechanism remains obscure. The collagen receptor such as discoidin domain receptor 1 and matrix metalloproteinase (MMP) play a significant role in inner ear structure and function. We hypothesize that HHcy increases hearing thresholds by compromise in inner ear vasculature resulted from impaired Hcy metabolism, increased oxidative stress, collagen IVa and collagen Ia turnover. The treatment with folic acid (FA) protects elevated hearing thresholds and prevents reduction in vessel density by lowering abundant collagen deposition and oxidative stress in inner ear. To test this hypothesis we employed 8 weeks old male wild type (WT), cystathionine-beta-synthase heterozygote knockout (CBS+/-) mice, WT + FA (0.0057 μg/g/day, equivalent to a 400 μg/70 kg/day human dose in drinking water); and CBS(+/-) +FA. The mice were treated for four weeks. The hearing thresholds were determined by recording the auditory brainstem responses. Integrity of vessels was analyzed by perfusion of horseradish peroxidase (HRP) tracer. Endothelial permeability was assessed, which indicated restoration of HRP leakage by FA treatment. A total Hcy level was increased in stria vascularis (SV) and spiral ligament (SL) of CBS+/- mice which was lowered by FA. Interestingly, FA treatment lowered Col IVa Immunostaining by affecting its turnover. The levels of MMP-2, -9, methylenetetrahydrofolate reductase (MTHFR) and cystathione gamma lyase (CSE) were measured by Western blot analysis. The oxidative stress was high in SV and SL of CBS+/- compared to WT however the treatment with FA lowered oxidative stress in CBS+/- mice. These data suggested that hearing loss in CBS+/- mice was primarily due to leakage in inner ear circulation, also partly by induced collagen imbalance, increase in Hcy and oxidative stress in inner ear.

Dietary intake of cholesterol is positively associated and use of cholesterol-lowering medication is negatively associated with prevalent age-related hearing loss

We aimed to assess associations between dietary intake of fats (saturated and monounsaturated fats and cholesterol) and certain food groups (butter, margarine, and nuts) with the prevalence, incidence, and progression of age-related hearing loss. We also aimed to investigate the link between serum lipids and cholesterol-lowering medication (statins) and hearing loss. The Blue Mountains Hearing Study is a population-based survey of age-related hearing loss. Hearing loss was measured in 2956 participants (aged ≥50 y) and was defined as the pure-tone average (PTA) of frequencies 0.5, 1.0, 2.0, and 4.0 kHz > 25 dB hearing level (PTA(0.5-4 kHz)). Dietary data were collected using a semiquantitative FFQ. After multivariable adjustment, the likelihood of prevalent hearing loss increased from the lowest (reference) to the highest quartile of dietary cholesterol intake (P-trend = 0.04). Among persons self-reporting statin use (n = 274), a 48% reduced odds of prevalent hearing loss was observed after multivariable adjustment [OR = 0.52 (95% CI = 0.29-0.93)]. Participants in the second and 3rd quartiles of dietary monounsaturated fat intake compared with those in the first quartile (reference) had a significantly reduced risk of hearing loss progression 5 y later [multivariable-adjusted OR = 0.39 (95% CI = 0.21-0.71)] and [OR = 0.51 (95% CI = 0.29-0.91)], respectively. Our results suggest that a diet high in cholesterol could have adverse influences on hearing, whereas treatment with statins and consumption of monounsaturated fats may have a beneficial influence.