Nobutaka Ohgami

BACKGROUND: People worldwide are routinely exposed to tellurium mainly via dietary ingestion. There has been no study to clarify the contribution of tellurium to blood pressure in humans or animals. METHODS: In this cross-sectional study conducted in a general population of 2592 residents in Japan, the associations of urinary tellurium levels with blood pressure and prevalence of hypertension were investigated. The potential sources of tellurium were also investigated. An interventional study in mice confirmed the effect of tellurium exposure on blood pressure. RESULTS: Linear and logistic regression analyses with consideration of confounders including urinary sodium-potassium ratio showed significant positive associations of urinary tellurium level with prevalence of hypertension and blood pressure. Cereals/beans and vegetables/fruits were determined to be potential dietary sources of tellurium exposure. Intermediary analysis suggested that increased intake of cereals/beans, but not that of vegetables/fruits, is positively associated with the tellurium-mediated risk of hypertension. Correspondingly, the mouse study showed that exposure to a putative human-equivalent dose of tellurium via drinking water increased blood pressure with an elevated level of urinary tellurium. The temporally increased blood pressure was decreased to the normal level by a break of tellurium exposure with a reduced level of urinary tellurium. CONCLUSIONS: The interdisciplinary approach provided the first evidence that tellurium exposure is a potential risk for increase of blood pressure. Since the human urinary tellurium level in this study is comparable with the levels in general populations in other Asian and European countries in previous studies, exposure to tellurium may be a latent universal risk for hypertension.

AIMS: There has been a shortage of human studies to elucidate the association between serum arsenic levels and the prevalence of hypertension. This study multidirectionally investigated associations among arsenic exposure, dietary ingestion, and the risk of hypertension by combined human epidemiological and mouse experimental studies. METHODS AND RESULTS: This study focused on the total arsenic level in fasting serum, a biomarker of arsenic exposure. Associations among ingestion frequencies of 54 diet items of Japanese food separated into six categories, total arsenic level in fasting serum, and the prevalence of hypertension were investigated in 2709 general people in Japan. Logistic regression analysis demonstrated a dose-dependent association between serum arsenic level and hypertension and a positive association between the ingestion of fish meat and hypertension. Further analysis showed that the latter association was fully mediated by increased fasting serum arsenic levels in humans. Similarly, oral exposure to the putative human-equivalent dose of arsenic species mixture with the same ratios in a common fish meat in Japan increased systolic blood pressure and arsenic levels in fasting serum in mice. CONCLUSION: This interdisciplinary approach suggests that fish-meat ingestion is a potential risk factor for arsenic-mediated hypertension. Because the increased consumption of fish meat is a recent global trend, health risks of the increased ingestion of arsenic via fish meat should be further investigated.

Ovarian cancers derived from endometrial cysts, also known as endometriosis in ovaries, are widespread histological types in Japan. Several studies suggest that zinc deficiency plays a role in endometriosis; however, the biological mechanism of zinc deficiency and endometrial cyst remains unknown. Thus, we investigated the association between zinc status and endometrial cysts. We measured the serum zinc levels in patients who had undergone surgery for endometrial cysts (n=19) and non-endometrial benign cysts (n=36). We analyzed cell proliferation, microarray data, and gene expression using N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a zinc chelator, in human immortalized endometrial epithelial cells (EMosis). The endometrial cyst group had considerably lower serum zinc levels than the non-endometrial benign cyst group. After adjusting for age, body mass index, alcohol consumption, smoking, and supplement use, endometrial cysts were markedly associated with serum zinc levels. EMosis cells treated with 5 μM TPEN demonstrated extensively increased proliferation compared to untreated cells. In the microarray analysis of EMosis cells treated with 5 μM TPEN, the enriched cellular components contained nucleoplasm, nuclear parts, and nuclear lumen. The upregulated biological processes included responses to hypoxia and decreased oxygen levels. The upregulated Kyoto Encyclopedia of Genes and Genomes pathway included the hypoxia-inducible factor-1 signaling pathway. EMosis cells treated with 5 μM TPEN demonstrated increased activator 1 (SRA1) expression and decreased AT-rich interaction domain 1A (ARID1A) expression. Protein-protein interaction network analysis indicated that ARID1A and SRA1 were associated with SMARCD1 and ATF1 among the differentially expressed genes in the microarray. EMosis cells treated with 5 μM TPEN revealed increased SRA1 mRNA levels and decreased ARID1A mRNA expression, whereas EMosis cells treated with 5 μM TPEN together with 10 μM zinc did not reveal changes in the mRNA levels of SRA1 or ARID1A compared with those without TPEN. These results suggest that zinc deficiency contributes to endometrial cyst development. Accordingly, zinc supplementation may suppress endometrial cyst development.

Harmful health effects of exposure to low-frequency noise (LFN) defined as noise with frequencies at ≤100 Hz on the circulatory system have been a concern. However, there has been no study on the effects of exposure to LFN on the circulatory system with consideration of its frequencies and decibels. In this study, the effects of short-term exposure to broad-band LFNs and their pure-tone components (pure-tone LFNs) on cutaneous blood flow in the extremities including the hands were investigated. In our fieldwork study, we first sampled some kinds of common broad-band LFNs. Our human study then showed that broad-band LFN with a narrower frequency range more strongly increased cutaneous blood flow than did broad-band LFN with a wider frequency range. Pure-tone LFNs of 70-100 Hz at ≤85 dB(Z), but not pure-tone LFNs exceeding 100 Hz, further increased levels of cutaneous blood flow. Our wavelet-transform spectrum analysis of cutaneous blood flow next revealed that the nitric oxide (NO)-dependent and -independent vascular activities of the vascular endothelium were specifically increased by exposure to pure-tone LFN. Our animal study again indicated that exposure to pure-tone LFN increased cutaneous blood flow in mice with impairments of bilateral inner ears as well as cutaneous blood flow in control mice, suggesting a limited effect of inner ear function on the LFN-mediated increase in cutaneous blood flow. The NO-dependent suppressive effect of pure-tone LFN on cutaneous blood flow was confirmed by inhibition of vascular endothelial activity through intravenous injection of an NO inhibitor in wild-type mice. Taken together, the results of this study demonstrated that the vascular endothelium is a target tissue of LFN and that NO is an effector of the LFN-mediated increase in cutaneous blood flow. Since improvement of peripheral circulation could generally promote human health, short-term exposure to LFN may be beneficial for health.

Hexavalent chromium [Cr(VI)], which has a strong corrosive effect, has been reported to cause perforation of the eardrum. Trivalent chromium [Cr(III)] also has a weak corrosive effect. However, there has been no study on the effects of exposure to Cr, either Cr(VI) or Cr(III), on hearing levels in animals or humans. In this study, the effect of Cr(III) exposure on hearing levels was determined in a human study. Then the reproducibility of the results obtained in the human study and the etiology were investigated in an animal study. The mean levels of total chromium (t-Cr) in hair and toenails from 100 Bangladeshi tannery workers were >20-fold and >360-fold higher, respectively, than those in hair and toenails from 49 Bangladeshi non-tannery workers (office workers). Multivariate analysis revealed decreases of hearing levels (DHLs) at 1 k and 4 k Hz, frequencies that are crucial for understanding language, but not at 8 k and 12 k Hz, in the tannery workers. Since >99.99% of t-Cr in the wastewater that the workers were in direct contact with in the tanneries was Cr(III), the epidemiological results suggest Cr(III)-mediated DHLs in the tannery workers. The results of animal experiments in this study further showed that treatment with eardrops but not intraperitoneal injection with the same amount of Cr(III) that tannery workers might be exposed to resulted in DHL with a damaged eardrum in mice. Previous studies suggested that Cr(III) can directly reach the eardrums of tannery workers via droplets in the air. Cr(III) could also reach the eardrum via picking an ear canal with a finger contaminated with tannery wastewater including Cr(III). Taken together, the results of both human and animal studies suggest the risk of DHLs caused by damage of the eardrum through external exposure to Cr(III) via the ear canal.

BACKGROUND: Air pollutants are suspected to affect pathological conditions of allergic rhinitis (AR). OBJECTIVES: After detecting Pb (375 μg/kg) in Japanese cedar pollen, the effects of intranasal exposure to Pb on symptoms of AR were investigated. METHODS: Pollen counts, subjective symptoms, and Pb levels in nasal epithelial lining fluid (ELF) were investigated in 44 patients with Japanese cedar pollinosis and 57 controls from preseason to season. Effects of intranasal exposure to Pb on symptoms were confirmed by using a mouse model of AR. RESULTS: Pb levels in ELF from patients were >40% higher than those in ELF from control subjects during the pollen season but not before the pollen season. Pb level in ELF was positively associated with pollen counts for the latest 4 days before visiting a hospital as well as scores of subjective symptoms. Intranasal exposure to Pb exacerbated symptoms in allergic mice, suggesting Pb as an exacerbation factor. Pb levels in ELF and nasal mucosa in Pb-exposed allergic mice were higher than those in Pb-exposed nonallergic mice, despite intranasally challenging the same amount of Pb. Because the increased Pb level in the nasal mucosa of Pb-exposed allergic mice was decreased after washing the nasal cavity, Pb on the surface of but not inside the nasal mucosa may have been a source of increased Pb level in ELF of allergic mice. CONCLUSIONS: Increased nasal Pb level partially derived from pollen could exacerbate subjective symptoms of AR, indicating Pb as a novel hazardous air pollutant for AR.

Hair graying is a representative sign of aging in animals and humans. However, the mechanism for hair graying with aging remains largely unknown. In this study, we found that the microscopic appearance of hair follicles without melanocyte stem cells (MSCs) and descendant melanocytes as well as macroscopic appearances of hair graying in RET-transgenic mice carrying RET oncogene (RET-mice) are in accordance with previously reported results for hair graying in humans. Therefore, RET-mice could be a novel model mouse line for age-related hair graying. We further showed hair graying with aging in RET-mice associated with RET-mediated acceleration of hair cycles, increase of senescent follicular keratinocyte stem cells (KSCs), and decreased expression levels of endothelin-1 (ET-1) in bulges, decreased endothelin receptor B (Ednrb) expression in MSCs, resulting in a decreased number of follicular MSCs. We then showed that hair graying in RET-mice was accelerated by congenitally decreased Ednrb expression in MSCs in heterozygously Ednrb-deleted RET-mice [Ednrb(+/-);RET-mice]. We finally partially confirmed common mechanisms of hair graying with aging in mice and humans. Taken together, our results suggest that age-related dysfunction between ET-1 in follicular KSCs and endothelin receptor B (Ednrb) in follicular MSCs via cumulative hair cycles is correlated with hair graying with aging.

BACKGROUND: The process for leather material production is carried out in developing countries using a large amount of trivalent chromium [Cr(III)]. Assesment of health risks for millions of workers in tanneries worldwide that are highly polluted with Cr(III) is needed. METHODS: Levels of total Cr and its chemical species in wastewater samples from tannery built-up areas of Bangladesh were investigated. Cr-mediated renal damage was assessed in 100 male tannery workers by epidemiological analysis consisting of questionnaires and measurements of levels of urinary Cr and urinary renal damage markers [urinary levels of total protein and kidney injury molecule-1 (KIM-1)]. RESULTS: High levels of total Cr (mean ± standard deviation = 1,908,762 ± 703,450 μg/L) were detected in wastewater samples from 13 sites of tanneries. More than 99.99% of total Cr in the wastewater was Cr(III), indicating that workers in the tanneries were exposed to large concentrations of Cr(III). Cr levels (mean ± standard, 2.89 ± 4.23 μg/g creatinine) in urine samples from the workers in tanneries were >24-fold higher than the levels in a general population previously reported. Multivariate analysis showed significant correlations between urinary levels of Cr and urinary levels of renal damage biomarkers. Nagelkerke Pseudo R2 values also showed that Cr level is the strongest contributor to the levels of renal damage biomarkers in the workers. CONCLUSION: Our results newly suggest that excess exposure to Cr(III) could be a risk for renal damage in humans.

Well water could be a stable source of drinking water. Recently, the use of well water as drinking water has been encouraged in developing countries. However, many kinds of disorders caused by toxic elements in well drinking water have been reported. It is our urgent task to resolve the global issue of element-originating diseases. In this review article, our multidisciplinary approaches focusing on oncogenic toxicities and disturbances of sensory organs (skin and ear) induced by arsenic and barium are introduced. First, our environmental monitoring in developing countries in Asia showed elevated concentrations of arsenic and barium in well drinking water. Then our experimental studies in mice and our epidemiological studies in humans showed arsenic-mediated increased risks of hyperpigmented skin and hearing loss with partial elucidation of their mechanisms. Our experimental studies using cultured cells with focus on the expression and activity levels of intracellular signal transduction molecules such as c-SRC, c-RET, and oncogenic RET showed risks for malignant transformation and/or progression arose from arsenic and barium. Finally, our original hydrotalcite-like compound was proposed as a novel remediation system to effectively remove arsenic and barium from well drinking water. Hopefully, comprehensive studies consisting of (1) environmental monitoring, (2) health risk assessments, and (3) remediation will be expanded in the field of environmental health to prevent various disorders caused by environmental factors including toxic elements in drinking water.

Health risks attributed to low-frequency noise (LFN) exposure are a serious global issue. Therefore, the development of a method for a prevention based upon risk assessments for LFN is important. Previously in vivo exposure of mice to LFN at 100 Hz, 95 dB for 1 hr produced imbalance with breakage of the otoconial membrane, which covers hair cells as well as impaired activity of hair cells in the vestibule. However, methods for inhibition of LFN-mediated imbalance have not been developed. At present, there are no apparent techniques available with in vitro or ex vivo assessments to evaluate LFN-mediated imbalance by direct administration of preventive chemicals into the vestibule. Our findings demonstrated the usefulness of an explant culture of the utricle with a fluorescent styryl dye, FM1-43FX. In addition, examination of the morphology of the otoconial membrane with explant cultures of utricles was conducted to determine the risk of LFN. Ex vivo exposure of the utricle to LFN at 100 Hz, 95 dB for 1 hr induced breaks in the otoconial membrane as well as decreased uptake of FM1-43FX in hair cells. Taken together, the results of this study provide a novel technique for assessing the risk of LFN exposure using an ex vivo experiment.

Chemical leukoderma is a patchy hypopigmentation in the skin. Phenol derivatives such as raspberry ketone have been reported to cause the development of occupationally induced leukoderma. Recently, 2% (w/w) rhododenol, a reduced form of raspberry ketone used in a skin-lightning agent, also caused the development of leukoderma in >16,000 users, about 2% of all users, in Asian countries including Japan. However, a method for assessing the risk of leukoderma caused by 2% rhododenol has not been established despite the fact that the development of leukoderma caused by 30% rhododenol was previously shown in animal experiments. Establishment of a novel technique for risk assessment of leukoderma in humans caused by external treatment with chemicals is needed to prevent a possible future chemical disaster. This study demonstrated that external treatment with 2% rhododenol and the same concentration of raspberry ketone caused the development of leukoderma in murine tail skin without exception with significant decreases in the amount of melanin and number of melanocytes in the epidermis. Thus, a novel in vivo technique that can assess the risk of leukoderma caused by 2% rhododenol was developed. The unique technique using tail skin has the potential to prevent chemical leukoderma in the future.

About 80% of young people use personal listening devices (PLDs) including MP3 players to listen to music, which consists of sound components with various frequencies. Previous studies showed that exposure to noise of high intensities affected balance in humans. However, there is no information about a frequency-dependent effect of sound components in music from a PLD on balance in young people. In this study, we determined the associations between sound component levels (dB) at 100, 1000 and 4000 Hz in music from a portable listening device (PLD) and balance objectively determined by posturography in young adults (n = 110). We divided the subjects into two groups (low and high exposure groups) based on cut-off values of sound component levels at each frequency using receiver operating characteristic (ROC) curves. Balance in the high exposure group (≥46.6 dB) at 100 Hz was significantly better than that in low exposure group in logistic regression models adjusted for sex, BMI, smoking status and alcohol intake, while there were no significant associations at 1000 and 4000 Hz. Thus, this study demonstrated for the first time that the sound component at 100 Hz with more than 46.6 dB in music improved balance in young adults.

Previous studies showed that people in urban areas are possibly exposed to 60–110 dB of low frequency noise (LFN) defined as noise of ≤100 Hz in their daily life. Previous studies also showed increased health risks by exposure to high levels (130–140 dB) of LFN in animals. However, little is known about the health effects of exposure to an ordinary level of LFN. We biochemically and immunohistochemically assessed the effects of exposure to inaudible LFN for mice (12 h/day of 100 Hz LFN at 95 dB for 5 days), at a level to which people are possibly exposed in daily life, on a murine inner ear by targeting 9 stress-reactive molecules. There was more than a 5-fold increased transcript level of heat shock protein 70 (Hsp70) in the whole inner ear exposed to LFN. However, the transcript levels of the other 8 stress-reactive molecules including Hsp27 and Hsp90 were comparable in LFN-exposed and unexposed murine inner ears. Only the transcript level of Cebpβ among the previously reported 4 transcriptional activators for Hsp70 expression was more than 3-fold increased by LFN exposure. Hsp70 transcript expression levels in the inner ears 3 days after LFN exposure were comparable to those in unexposed inner ears. The protein level of Hsp70, but not the levels of Hsp27 and Hsp90, was also increased in the vestibule by LFN exposure. However, hearing levels as well as expression levels of Hsp70 protein in the cochleae were comparable in LFN-exposed mice and unexposed mice. Our results demonstrated that the inner ear might be one of the organs that is negatively affected by stress from inaudible LFN exposure. Moreover, LFN exposure might increase Hsp70 expression level via Cebpβ in the inner ear. Thus, Hsp70 and Cebpβ levels could be candidates of biomarkers for response to LFN exposure.

There is no information on the association between oral exposure to arsenic (As) and hearing loss in humans or mice. In this combined epidemiological study and experimental study, the association of oral exposure to As with hearing loss in people aged 12-29 years and young mice was examined. Subjects in the exposure group (n = 48), who were drinking tube well water contaminated with As, showed significantly higher risks of hearing loss at 4 kHz [odds ratio (OR) = 7.60; 95% confidence interval (CI): 1.56, 57.88], 8 kHz (OR = 5.00; 95% CI: 1.48, 18.90) and 12 kHz (OR = 8.72; 95% CI: 2.09, 47.77) than did subjects in the control group (n = 29). We next performed an experiment in which young mice were exposed to As via drinking water at 22.5 mg/L, which is a much greater concentration than that in human studies. The exposure group showed hearing loss and accumulation of As in inner ears. Ex vivo exposure of the organ of Corti from mice exposed to As significantly decreased the number of auditory neurons and fibers. Thus, our combined study showed that oral exposure to As caused hearing loss in young people and young mice.

General electric devices and ventilation systems are known to generate low frequency noise (LFN) with frequencies of <100 Hz. Previous studies showed that exposure to LFN caused impairments of balance in humans and mice during adulthood. On the other hand, a previous study showed that noise levels in the neonatal intensive care unit (NICU) were greater than those in general home or office environments. Therefore, it is possible that neonates have a potential risk to be exposed to LFN in the NICU. However, the risk of neonatal exposure to LFN remains unclear in humans and mice. In this study, male ICR mice were exposed to LFN at 100 Hz for 4 weeks after birth and then subjected to rotarod and beam crossing tests in order to assess LFN-mediated risk of imbalance during the neonatal period. Exposure to LFN at 70 dB, but not exposure to LFN up to 60 dB, during the neonatal period significantly decreased performance scores for rotarod and beam crossing tests compared to the scores of the control group. The number of calbindin-positive hair cells in the saccule and utricle was decreased in mice exposed to LFN at 70 dB for 4 weeks in the neonatal phase. Cessation of exposure for 10 weeks did not result in recovery of the decreased performance in rotarod and beam crossing tests. Thus, our results suggest that 70 dB is a possible threshold for exposure to LFN for 4 weeks during the neonatal period causing unrecoverable imbalance in mice.

Despite the fact that manganese (Mn) is known to be a neurotoxic element relevant to age-related disorders, the risk of oral exposure to Mn for age-related hearing loss remains unclear. In this study, we orally exposed wild-type young adult mice to Mn (Mn-exposed WT-mice) at 1.65 and 16.50 mg/L for 4 weeks. Mn-exposed WT-mice showed acceleration of age-related hearing loss. Mn-exposed WT-mice had neurodegeneration of spiral ganglion neurons (SGNs) with increased number of lipofuscin granules. Mn-exposed WT-mice also had increased hypoxia-inducible factor-1 alpha (Hif-1 alpha) protein with less hydroxylation at proline 564 and decreased c-Ret protein in SGNs. Mn-mediated acceleration of age-related hearing loss involving neurodegeneration of SGNs was rescued in RET-transgenic mice carrying constitutively activated RET. Thus, oral exposure to Mn accelerates age-related hearing loss in mice with Ret-mediated neurodegeneration of SGNs.

Our previous study experimentally showed barium (Ba)-mediated hearing loss in mice. To our knowledge, however, it remains unknown whether Ba affects hearing in humans. This epidemiological study aimed at investigating ototoxicity of Ba in humans. Associations of Ba levels in hair, toenails and urine with hearing levels (1, 4, 8 and 12 kHz) were analyzed in 145 Bangladeshi subjects. Binary logistic regression analysis with adjustment for age, sex, body mass index (BMI) and smoking showed that Ba levels in hair had significant associations with hearing loss at 8 kHz (OR = 4.75; 95% CI: 1.44, 17.68) and 12 kHz (OR = 15.48; 95% CI: 4.04, 79.45). Ba levels in toenails were also associated with hearing loss at 8 kHz (OR = 3.20; 95% CI: 1.35, 7.85) and 12 kHz (OR = 3.63; 95% CI: 1.58, 8.55), whereas there was no correlation between Ba level in urinary samples and hearing. There was a significant correlation between hearing loss and Ba levels in hair and toenails in the model adjusted with arsenic levels as the confounder. In conclusion, this study suggested that Ba levels could be a new risk factor for hearing loss, especially at high frequencies of 8 and 12 kHz, in humans.

We showed that 2.1% of 233 pieces of lumber debris after the Great East Japan Earthquake was chromated copper arsenate (CCA)-treated wood. Since hexavalent chromium (Cr), copper (Cu) and pentavalent arsenic (As) in the debris may be diffused in the air via incineration, we exposed human lung normal (BEAS-2B) and carcinoma (A549) cells to Cr, Cu and As at the molar ratio in a representative CCA-treated wood. Co-exposure to 0.10 mu M Cr and 0.06 mu M As, which solely had no effect on colony formation, synergistically promoted colony formation in BEAS-28 cells, but not A549 cells, with activation of the PI3K/AKT pathway. Sole exposure and co-exposure to Cu showed limited effects. Since previous reports showed Cr and As concentrations to which human lungs might be exposed, our results suggest the importance to avoid diffusion of Cr and As in the air via incineration of debris including CCA-treated wood after the disaster. (C) 2015 Elsevier Ltd. All rights reserved.

Purpose: We continuously ingest barium as a general element by drinking water and foods in our daily life. Exposure to high-dose barium (>100 mg/kg/day) has been shown to cause physiological impairments. Direct administration of barium to inner ears by vascular perfusion has been shown to cause physiological impairments in inner ears. However, the toxic influence of oral exposure to low-dose barium on hearing levels has not been clarified in vivo. We analyzed the toxic influence of oral exposure to low-dose barium on hearing levels and inner ears in mice. Experimental design: We orally administered barium at low doses of 0.14 and 1.4 mg/kg/day to wild-type ICR mice by drinking water. The doses are equivalent to and 10-fold higher than the limit level (0.7 mg/l) of WHO health-based guidelines for drinking water, respectively. After 2-week exposure, hearing levels were measured by auditory brain stem responses and inner ears were morphologically analyzed. After 2-month exposure, tissue distribution of barium was measured by inductively coupled plasma mass spectrometry. Results: Low-dose barium in drinking water caused severe hearing loss in mice. Inner ears including inner and outer hair cells, stria vascularis and spiral ganglion neurons showed severe degeneration. The Barium-administered group showed significantly higher levels of barium in inner ears than those in the control group, while barium levels in bone did not show a significant difference between the two groups. Barium levels in other tissues including the cerebrum, cerebellum, heart, liver and kidney were undetectably low in both groups. Conclusions: Our results demonstrate for the first time that low-dose barium administered by drinking water specifically distributes to inner ears resulting in severe ototoxicity with degeneration of inner ears in mice. (C) 2012 Elsevier Inc. All rights reserved.

There have been few reports showing a correlation between hearing levels and life style in young people. In this study, we succeeded in sensitively evaluating hearing levels in 51 young male adults of 21 - 23 years in age by 12 k Hz extra-high-frequency auditory thresholds, which cannot be measured by usual audiometry devices for clinical use. Noise exposure, alcohol consumption and sleeping time did not affect hearing levels in young adults. Auditory thresholds of 12 kHz frequency in smokers were significantly (p < 0.05) higher than those in non-smokers, while there were no differences in 1 kHz, 4 kHz and 8 kHz frequencies of hearing levels between smokers and non-smokers. Since the Brinkman Index (BI; cigarettes/day multiplied by number of years) of smokers in this study was from 12 to 60, our results suggest that even light smoking of less than 20 cigarettes/day for 3 years can result in the development of hearing loss of 12 kHz frequency in young adults. Binary logistic regression analysis again showed a correlation between hearing loss (>= 40 dB of auditory thresholds in 12 kHz frequency) and light smoking (12 <= BI <= 60). Thus, this study showed that auditory threshold at 12 kHz frequency could be a sensitive marker for hearing in young adults. More importantly, we for the first time provided epidemiological evidence that light smoking might affect hearing level at 12 kHz frequency and revealed a new risk of light smoking.

A significantly increased risk for dominant sensorineural deafness in patients who have Hirschsprung disease (HSCR) caused by endothelin receptor type B and SOX10 has been reported. Despite the fact that c-RET is the most frequent causal gene of HSCR, it has not been determined whether impairments of c-Ret and c-RET cause congenital deafness in mice and humans. Here, we show that impaired phosphorylation of c-Ret at tyrosine 1062 causes HSCR-linked syndromic congenital deafness in c-Ret knockin (KI) mice. The deafness involves neurodegeneration of spiral ganglion neurons (SGNs) with not only impaired phosphorylation of Akt and NF-kappa B but decreased expression of calbindin D28k in inner ears. The congenital deafness involving neurodegeneration of SGNs in c-Ret KI mice was rescued by introducing constitutively activated RET. Taken together with our results for three patients with congenital deafness with c-RET-mediated severe HSCR, our results indicate that c-Ret and c-RET are a deafness-related molecule in mice and humans.