- Email: [email protected]
Role of free oxygen radicals in noise-related hearing impairment
Hearing Research 162 (2001) 43^47 www.elsevier.com/locate/heares
Role of free oxygen radicals in noise-related hearing impairment Içrfan Kaygusuz a
a;
ë ztu«rk a , Bilal U ë stu«ndag¯ b , S°inasi Yalc°in *, Ahmet O
a
Department of Otorhinolaryngology, F|rat University, Medical Faculty, 23200 Elaz|g¯, Turkey b Department of Biochemistry, F|rat University, Medical Faculty, 23200 Elaz|g¯, Turkey Received 6 March 2001; accepted 8 August 2001
Abstract This study was aimed at defining the relationship between noise-related hearing impairment in industrial workers exposed to continuous noise. For this malondialdehyde and glutathione peroxidase were analyzed as free radical form and antioxidant form. A total of 60 patients working in the units of a hydroelectric power plant were included in the study. This experimental group was further divided into three subgroups of 20 workers, each group exposed to a different noise level. The control group consisted of 20 male volunteers employed in the Medical Centre where the study was carried out. A standard ascending/descending method was applied to the subjects of the experimental and the control groups in order to determine their hearing thresholds at seven different frequencies between 250 and 8000 Hz. Then, 10 ml blood was collected from each person to measure the malondialdehyde values in plasma and glutathione peroxidase activity in erythrocytes. Slight sensorineural hearing impairment was found in group I beginning at 4 kHz and in group II beginning at 6 kHz. Statistically significant differences were observed in group I and II when compared to the control group (P 6 0.05). It was found that malondialdehyde levels increased in the experimental groups more than in the control groups. However, this increase was only significant in group I (P 6 0.05). Erythrocyte glutathione peroxidase activity significantly increased in group I and II compared to the other groups (P 6 0.05), also, the difference was significant between group I and II (P 6 0.05). Accordingly, it is suggested that free oxygen radicals may take a role in noise-related hearing impairment. ß 2001 Elsevier Science B.V. All rights reserved. Key words: Hearing impairment; Noise ; Free oxygen radicals scavenging; Antioxidant
1. Introduction Noise-related hearing impairment has been diagnosed since the beginning of written history and studies have begun to ¢nd ways of protecting from noise and providing suitable treatment (Alberti, 1997). Although deafness has been reported among those who lived near the Nile falls in the ¢rst century A.D., it was initially used as a standard term of diagnosis for boiler workers in 1850 (Ward, 1991). Among vocational damages, the noise-related hearing impairment was the most common cause. It has been reported that 7.4^10.2 million industrial workers are at risk for hearing impair-
* Corresponding author. Tel.: +90 (424) 233 35 55; Fax: +90 (424) 238 80 96. E-mail address: [email protected] (I. Kaygusuz).
ment in the USA (Seidman et al., 1993). In 1896, Habermann proved the destruction of the Corti organ due to industrial noise (Ward, 1991 ; Hawkins, 1971). As a result of long-term exposure to noise, capillary spiral lamina and the lateral wall of the blood veins of cochlea are damaged (Nakai and Masutani, 1988). Recently, the in£uence of free oxygen radicals in tissue damage has been shown and discussions have been focused on the e¡ect of noise-related free oxygen radicals in cochlear damage. It has been reported that the increase in free oxygen radical formation and activity may lead to damage in cochlear sensory epithelium resulting in change of hearing threshold (Seidman et al., 1993 ; Liu, 1992). This study was performed to investigate the relationship between noise-related hearing impairment of industrial workers being exposed to long-term continuous noise and free oxygen radicals.
0378-5955 / 01 / $ ^ see front matter ß 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 5 9 5 5 ( 0 1 ) 0 0 3 6 5 - 3
HEARES 3763 5-11-01
44
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
2. Materials and method The present study was performed on a total of 60 patients, at F|rat Medical Centre ENT Clinic, F|rat University. The design of this study has been approved by the Ethical Committee of the F|rat University. 2.1. Experimental group This study consisted of 75 male workers employed in the noisy units of a hydroelectric power plant. In anamnesis, they were asked whether they had a current or past hearing disorder. None of the subjects had any known pathologies at the time of the experiment. Meanwhile, smokers and alcohol users were avoided. Fifteen workers were excluded because they did not meet the study criterions. To determine the hearing thresholds at 250, 500, 1000, 2000, 4000, 6000 and 8000 Hz, a standard ascending/descending method was applied to the 60 workers who had no hearing disorder, no pathology in otoscopic examination and having a normal tympanometry. To avoid the possible e¡ect of temporary threshold shift on permanent threshold shift, all tests were performed after at least 18 h of noise-free period (Yellin, 1991). The experimental group was divided into three subgroups according to the areas that the workers were employed in. 2.2. Group I (turbine group) Consisted of 20 workers who worked without protection for 8 h a day in the turbine part of the hydroelectric power plant where there is a continuous noise level of 95^110 dB. 2.3. Group II (machinery maintenance workshop group) Consisted of 20 workers who worked without protection for 8 h a day in the generator room or machine room of the hydroelectric power plant where the continuous noise level was 75^85 dB. 2.4. Group III (outdoor experimental group) Consisted of 20 workers who worked in the open areas of the hydroelectric power plant where the continuous noise level was below 75 dB. 2.5. Control group Consisted of 20 male volunteers employed in the Medical Centre where the study was conducted. The inclusion criterions were: no pathology in otoscopic examinations, having a normal tympanometry and a
normal hearing threshold at all frequencies between 250 and 8000 Hz indicated in audiograms. 2.6. Audiologic tests They were carried out in standard acoustically controlled rooms (Industrial Acoustics Company) using Interacoustics Clinical Computer Audiometer Model AC5, Interacoustics Impedance Audiometer AZ7 and Interacoustics XYT Recorder Model AG3, (Interacoustics, Assens, Denmark). The audiometer was calibrated by a Bruel-Kjaer Type 4144 microphone, Type 1613 audio frequency spectrometer and 6 cc arti¢cial ear plug. Noise levels in di¡erent units of the hydroelectric power plant were measured using a noise meter (Bruel Kjaer 2235, Copenhagen, Denmark). 2.7. Biochemical assessments Blood samples (10 ml) were taken under sterile conditions in tubes with ethylenediaminetetraacetic acid from each of the subjects in the experimental and control groups. Samples were centrifuged at 3000 rpm for 10 min and the plasma was used to measure malondialdehyde (MDA) levels, and erythrocytes were used to measure glutathione peroxidase (GSH-Px) activity. MDA was measured by a spectrophotometer (Schimadzu UV-1201 Spectrophotometer, Schimadzu Corp., Japan) using a method modi¢ed from Satoh (1978) and Yagi (1984) ; GSH-Px activity was measured using the method of Paglia and Valentine (1967) based on the oxidation of NADPH by glutathione reductase enzyme. 2.8. Statistical analysis One-way variance analysis and Tukey's HSD test were used. 3. Results The mean age of 60 workers working in the noise parts of the hydroelectric power plant for 14.21 þ 6.11 years was 28^49 years (37.7 þ 5.6) and the age range of the control group was 28^48 (mean 36.8 þ 4.5). The audiometric data including the hearing thresholds in dB nHL of the control and experiment groups at seven di¡erent frequencies between 250 and 8000 Hz, and their statistical comparison is shown in Table 1. Mean pure tone audiometric thresholds in group I and II with noise-induced hearing loss were signi¢cantly higher than in those of group III and control subjects at octave frequencies in the range of 2^8 kHz. Hearing
HEARES 3763 5-11-01
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
45
Table 1 Hearing threshold averages, standard deviations and statistical comparison of the experiment and control groups Test frequency (Hz)
Group I
Group II
Group III
Control
250 500 1000 2000* 4000* 6000* 8000*
13.5 þ 4.1 12.9 þ 5.6 13.4 þ 4.8 20.6 þ 9.0# 25.6 þ 12.2# 37.6 þ 15.49 30.2 þ 18.19
11.9 þ 6.3 13.4 þ 8.4 13.5 þ 7.7 18.0 þ 8.6i 19.5 þ 9.8i 26.1 þ 10.2i 20.5 þ 11.3
11.5 þ 3.8 11.1 þ 4.9 11.2 þ 4.5 12.6 þ 6.1 13.8 þ 5.9 15.5 þ 4.2 14.1 þ 11.2
8.1 þ 4.7 9.3 þ 5.5 9.9 þ 7.8 10.2 þ 5.6 11.3 þ 8.8 14.5 þ 6.2 13.5 þ 7.6
*P 6 0.0001 (one-way analysis of variance); #P 6 0.05 (Tukey's HSD test), compared group I with control and group III; iP 6 0.05 (Tukey's HSD test), compared group II with control and group III; 9P 6 0.05 (Tukey's HSD test), compared group I with control, group II and group III.
losses were more evident at 6 kHz than at 2, 4 and 8 kHz. The level of MDA and GSH-Px of the control and the experimental groups with associated statistical comparison is summarized in Table 2. MDA levels were higher in the experimental groups versus the control group. MDA levels of the experimental groups increased, but only the MDA level of group I was signi¢cantly di¡erent from the other groups (P 6 0.05). GSHPx activity was the highest in group I. It was signi¢cantly di¡erent in groups I and II versus the control group and group III. The di¡erence was also signi¢cant when comparison was made between group I and II (P 6 0.05). 4. Discussion With the exception of presbycusis, the most common reason of sensorineural hearing impairment is noise (Dobie, 1995). It has been known for many years that high levels of noise cause permanent damage to the hearing mechanism. The adverse a¡ect of noise on hearing depends on the degeneration and damage of internal hair cells in the basal coil of the Corti organ. The audiological indicator of it is the bilateral, symmetric, sensorineural type hearing impairment seen around 3^6 kHz (Ward, 1991). The severity, frequency, duration and temporal characteristics (continuous, £uctuating, intermittent) of the noise are important factors affecting the cochlear damage (Attias and Pratt, 1985 ; Osguthorpe and Klein, 1991).
Although each individual is di¡erently a¡ected by the noise, there are several other important factors. The ¢rst one is the period during which the person works continuously and the second one is being in the same environment for years. Being exposed to 100 dB of noise every day for a continuous period of 8 h initially results in a hearing impairment progressing fast around 4 kHz, but at frequencies under 4 kHz, no substantial change occurs. People working in noise environments have an impairment of 15^20 dB in the ¢rst 1^2 years and this level gradually increases in the ¢rst 10 years. Then, it slows or completely stops (Alberti, 1997). C°elik et al. (1996) have reported 1^8 kHz hearing impairment in the workers who have been exposed to 95^110 dB vocational noise for 1^20 years and has emphasized that hearing impairment was particularly obvious at 4^6 kHz. They have also noted that hearing impairment is highest in the ¢rst 10 years and then it begins to decrease. Seidman et al. (1993) have stated that free oxygen radicals are responsible for the noise-related damage in sensory epithelium and the damage might be prevented by using radical scavengers. In a study to investigate the noise-related free radical formation in cochlea, it was found a that superoxide anion radical was formed in the luminal membranes of stria vascularis of the marginal cells of guinea pigs which have been exposed to 120^125 dB of noise for 3 h (Yamene et al., 1995). This was believed to be the result of the increase in free radicals due to the ischemia-reperfusion occurring in the cochlear microcirculation because of the noise.
Table 2 MDA (nmol/ml) and GSH-Px (U/mgHb) averages, standard deviations and statistical comparisons of the control and experiment groups MDA GSH-Px
Group I
Group II
Group III
Control
0.54 þ 3.1*8 5.85 þ 1.1*v
0.39 þ 2.1* 5.18 þ 1.5*i
0.36 þ 1.8* 4.43 þ 1.1*
0.31 þ 2.3* 4.09 þ 2.3*
*P 6 0.0001 (one-way analysis of variance), 8 P 6 0.05 (Tukey's HSD test), compared group I, group II and group III with control; v P 6 0.05 (Tukey's HSD test), compared group I, group II and group III with control; i P 6 0.05 (Tukey's HSD test), compared group II and group III with control.
HEARES 3763 5-11-01
46
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
Herken et al. (2001) studied schizophrenic patients, whereas Licastro et al. (2001) and Mihailovic et al. (1998) examined patients with Alzheimer and chronic heart failure, respectively. They measured the level of activity of GSH-Px in peripheral blood and determined a correlation between the level of GSH-Px and these diseases. The method used in the present study and the results were well correlated with the literature in this aspect. Ising (2000) reported that noise caused an increase in the level of acute and chronic hormones and consequently, elevated levels of free oxygen radicals were observed. Similarly, it was shown that the level of these oxidant agents can also be measured in several other organs, i.e. liver. Salvi et al. (2001), reported detonation of enzymatic activity, biological function loss in protein transport and in receptors and determined the structural damages of proteins due to free radicals. Additionally, it was concluded that this structural damage can be prevented using antioxidant agents. Ohinata et al. (2000) investigated the noise-related hearing impairment and determined the correlation between auditory damage and reactive oxygen species. 8Isoprostan was studied biochemically and histochemically as a predictor of free oxygen radicals. It was reported that the level of 8-isoprostan increased in respect to the duration of the noise time. 8-Isoprostan levels were found to be increased in the organ of Corti, spiral ganglion cells and stria vascularis. With these data, they reported that free oxygen radicals played a role in the development of noise-associated auditory damage and determined the correlation between lipid peroxidation and noise-related damage in the organ of Corti. Although MDA is not a speci¢c or quantitative indicator of fatty acid oxidation, it has correlation with the level of lipid peroxidation. MDA accumulation, which is related to lipid peroxidation, is an important component of the damage that develops in the reperfusion phase (Halliwell, 1994). Liu (1992) has evaluated the changes in MDA levels of the cochlear tissue and auditory brainstem response hearing threshold in guinea pigs in order to investigate the role of free oxygen radicals in hearing impairment due to blast trauma. He has reported that in the ¢rst hours after blast trauma, MDA levels of the cochlea tissue begin to increase; MDA level is at peak on the 3rd and 6th days. Although it reaches to normal level on the 8th day, it reaches to a second peak on the 12th day, and hearing thresholds are proportional to MDA level. Based on these ¢ndings, it has been argued that hearing impairment related to blast trauma stems from the increase in free oxygen radicals reactions. The results of our study also support this conclusion that MDA levels increase proportionally with the increased level of noise-related hearing impairment.
Cells have antioxidant defence mechanisms that prevent, limit or partly repair oxidative damage. The most e¡ective defence mechanism is the enzyme systems. One of them is the GSH-Px enzyme which reduces the hydroxy peroxides to water at the expense of reduced glutathione. GSH-Px prevents the e¡ect of free radicals and protects the cell from damage (Halliwell, 1994). In an experimental study, Yamasoba et al. (1998) have discussed that noise increases the glutathione level in the lateral wall of the cochlea, and it does not change in modiolus or sensory epithelium. Accordingly, noise increases the selective glutathione synthesis in the lateral wall of the cochlea. Jacono et al. (1998) have reported that hair cell damage in the Corti organ decreases proportionally with the increase in glutathione levels and catalase levels in stria vascularis, and suggested that the glutathione enzyme system is a protective mechanism against the noise-related hearing impairment. In our study, we have also found that GSH-Px activity increases proportionally with the increased level of noise-related hearing impairment, although there is no statistically signi¢cant di¡erence between group III and the control group. It has been pointed out in many studies that, there is a role of the increased free radical formation to the cochlear damage during high-level noise. On the other hand, Ising and Braun (2000) have studied the e¡ects of acute and chronic noise on the endocrine system. Henry and Stephens (1977) have made a model for psychophysiological stress of noise. They have pointed out that three di¡erent reactions occurred in their experiment; (1) an increase of adrenaline and noradrenaline in suprarenal medulla in ¢ght^¢ght reaction, (2) hypothalamic pituitary adrenocortical system was inhibited and cortisol was increased within defeat reaction, (3) the expression of noradrenaline of sympathetic synapses was increased in workers supplied with noise higher than 90 dB in their environment. In this study, they have mentioned that stress hormones are increased in the blood by noise and the important e¡ect of chronic noise found in the unprotected workers is hypercortisolism. In our study, we have also noticed that noise is a very important stress factor and the activity of blood MDA and GSH-Px is increased in those people working in high-noise environments. In the same worker group, hearing defects were found especially at 6 kHz. Because noise-related hearing impairment can not be treated medically or by surgery, the main aim is to prevent cochlear damage caused by noise and to protect hearing ability. We have found that MDA and GSH-Px activity values increase progressively with the severity of noise, and with these changes the physiological protection mechanisms are e¡ective to a certain degree, however, that is not su¤cient. In conclusion, we suggest that the existing natural antioxidants in the cell are not
HEARES 3763 5-11-01
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
enough to prevent the noise-related damage and cochlear damage can be minimized by prescribing antioxidant drugs to those who work in noise environments. However, more data are needed at the biochemical and epidemiologic levels for a better understanding of these ¢ndings. References Alberti, P.W., 1997. Noise and the ear. In: Kerr, A.G., Dafyold, S., (Eds.), Scott-Brown's Otolaryngology. Reed Educational and Professional Publishing Ltd, Oxford, pp. 1^31. Attias, J., Pratt, H., 1985. Auditory evoked potential correlates of susceptibilty to noise induced hearing loss. Audiology 24, 149^156. ë ztu«rk, A., 1996. Hearing parameters in noise C°elik, O., Yalc°|n, S°., O exposed industrial workers. Auris Nasus Larynx 23, 127^132. Dobie, R.A., 1995. Prevention of noise-induced hearing loss. Arch. Otolaryngol. Head Neck Surg. 121, 385^391. Halliwell, B., 1994. Free radicals, antioxidants, and human disease: curiosity, cause, or consequence? Lancet 344, 721^724. Hawkins, J.E., 1971. The role of vasoconstriction in noise-induced hearing loss. Ann. Otol. Rhinol. Laryngol. 80, 903^913. Henry, J.P., Stephens, P.M., 1977. The social environment and essential hypertension in mice; possible role of the innervation of the adrenal cortex. Prog. Brain Res. 47, 263^267. Herken, H., Uz, E., Ozyurt, H., Sogut, S., Virit, O., Akyol, O., 2001. Evidence that the activities of erythrocyte free radical scavenging enzymes and the products of lipid peroxidation are increased in di¡erent forms of schizophrenia. Mol. Psychiatr. 6, 66^73. Ising, H., 2000. Acute and chronic stress hormone increases in noise exposure. Schr.reihe Ver. Wasser Boden Lufthyg. 106, 169^177. Ising, H., Braun, C., 2000. Acute and chronic endocrine e¡ects of noise: review of the research conducted at the Institute for Water, Soil and Air Hygiene. Noise Health 7, 7^24. Jacono, A.A., Hu, B., Kopke, R.D., Henderson, D., Van De Wetar, T.R., Steinman, H.M., 1998. Changes in cochlear antioxidant enzyme activity after sound conditioning and noise exposure in the chinchilla. Hear. Res. 117, 31^38. Licastro, F., Pedrini, S., Davis, L.J., Caputo, L., Tagliabue, J., Savorani, G., Cucinotta, D., Annoni, G., 2001. Alpha-1-antichymotrypsin and oxidative stress in the peripheral blood from patients with probable Alzheimer disease: a short-term longitudinal study. Alzheimer Dis. Assoc. Disord. 15, 51^55.
47
Liu, Z., 1992. Experimental study on the mechanism of free radical in blast trauma induced hearing loss. Zhonghua Er Bi Yan Hou Ke Za Zhi 27, 24^26. Mihailovic, M.B., Avramovic, D.M., Jovanovic, I.B., Pesut, O.J., Matic, D.P., Stojanov, V.J., 1998. Blood and plasma selenium levels and GSH-Px activities in patients with arterial hypertension and chronic heart disease. J. Environ. Pathol. Toxicol. Oncol. 17, 285^289. Nakai, Y., Masutani, H., 1988. Noise induced vasoconstriction in the cochlea. Acta. Otolarngol. 447 (Suppl.), 23^27. Ohinata, Y., Miller, J.M., Altschuler, R.A., Schacht, J., 2000. Intense noise induces formation of vasoactive lipid peroxidation products in the cochlea. Brain Res. 878, 163^173. Osguthorpe, J.D., Klein, A.J., 1991. Occupational hearing conservation. Otolaryngol. Clin. N. Am. 24, 403^414. Paglia, D.E., Valentine, W.N., 1967. Studies on the quantitative and qualitative characterization of erythtrocyte glutatione peroxidase. J. Lab. Clin. Med. 70, 158^169. Salvi, A., Carrupt, P.A., Tillement, J.P., Testa, B., 2001. Structural damage to proteins caused by free radicals: asessment, protection by antioxidants, and in£uence of protein binding. Biochem. Pharmacol. 61, 1237^1242. Satoh, K., 1978. Serum lipid peroxide in cerebrovascular disorders determined by a new colorimetric method. Clin. Chim. Acta 90, 37^43. Seidman, M.D., Sh|vapuja, B.G., Quirk, W.S., 1993. The protective e¡ects of allopurinol and superoxide dismutase on noise-induced cochlear damage. Otolaryngol. Head Neck Surg. 109, 1052^1056. Ward, W.D., 1991. Noise induced hearing damage. In: Paparella, M.M., Shumrick, D.A., Gluckman, J.L., Meyerho¡, W.L., (Eds.), Otolaryngology. WB Saunders Co., London, pp. 1639^ 1652. Yagi, K., 1984. Assay of lipid peroxidation in blood plasma or serum. Methods Enzymol. 105, 328^363. Yamasoba, T., Harris, C., Schoji, F., Lee, R.J., Nuttall, A.L., Miller, J.M., 1998. In£uence of intense sound exposure on glutathione synthesis in the cochlea. Brain Res. 804, 72^78. Yamene, H., Nakai, Y., Takayama, M., Konishi, K., Iguichi, H., Nakagawa, T., Shibata, S., Kato, A., Sunami, K., Kawakatsu, C., 1995. The emergence of free radicals after acoustic trauma and strial blood £ow. Acta. Otolaryngol. Stockholm 519 (Suppl.), 87^97. Yellin, M.W., 1991. Hearing measurment in adults. In: Paparella, M.M., Shumrick, D.A., Gluckman, J.L., Meyerho¡, W.L., (Eds.), Otolaryngology. WB Saunders Co., London, pp. 961^ 975.
HEARES 3763 5-11-01
Role of free oxygen radicals in noise-related hearing impairment Içrfan Kaygusuz a
a;
ë ztu«rk a , Bilal U ë stu«ndag¯ b , S°inasi Yalc°in *, Ahmet O
a
Department of Otorhinolaryngology, F|rat University, Medical Faculty, 23200 Elaz|g¯, Turkey b Department of Biochemistry, F|rat University, Medical Faculty, 23200 Elaz|g¯, Turkey Received 6 March 2001; accepted 8 August 2001
Abstract This study was aimed at defining the relationship between noise-related hearing impairment in industrial workers exposed to continuous noise. For this malondialdehyde and glutathione peroxidase were analyzed as free radical form and antioxidant form. A total of 60 patients working in the units of a hydroelectric power plant were included in the study. This experimental group was further divided into three subgroups of 20 workers, each group exposed to a different noise level. The control group consisted of 20 male volunteers employed in the Medical Centre where the study was carried out. A standard ascending/descending method was applied to the subjects of the experimental and the control groups in order to determine their hearing thresholds at seven different frequencies between 250 and 8000 Hz. Then, 10 ml blood was collected from each person to measure the malondialdehyde values in plasma and glutathione peroxidase activity in erythrocytes. Slight sensorineural hearing impairment was found in group I beginning at 4 kHz and in group II beginning at 6 kHz. Statistically significant differences were observed in group I and II when compared to the control group (P 6 0.05). It was found that malondialdehyde levels increased in the experimental groups more than in the control groups. However, this increase was only significant in group I (P 6 0.05). Erythrocyte glutathione peroxidase activity significantly increased in group I and II compared to the other groups (P 6 0.05), also, the difference was significant between group I and II (P 6 0.05). Accordingly, it is suggested that free oxygen radicals may take a role in noise-related hearing impairment. ß 2001 Elsevier Science B.V. All rights reserved. Key words: Hearing impairment; Noise ; Free oxygen radicals scavenging; Antioxidant
1. Introduction Noise-related hearing impairment has been diagnosed since the beginning of written history and studies have begun to ¢nd ways of protecting from noise and providing suitable treatment (Alberti, 1997). Although deafness has been reported among those who lived near the Nile falls in the ¢rst century A.D., it was initially used as a standard term of diagnosis for boiler workers in 1850 (Ward, 1991). Among vocational damages, the noise-related hearing impairment was the most common cause. It has been reported that 7.4^10.2 million industrial workers are at risk for hearing impair-
* Corresponding author. Tel.: +90 (424) 233 35 55; Fax: +90 (424) 238 80 96. E-mail address: [email protected] (I. Kaygusuz).
ment in the USA (Seidman et al., 1993). In 1896, Habermann proved the destruction of the Corti organ due to industrial noise (Ward, 1991 ; Hawkins, 1971). As a result of long-term exposure to noise, capillary spiral lamina and the lateral wall of the blood veins of cochlea are damaged (Nakai and Masutani, 1988). Recently, the in£uence of free oxygen radicals in tissue damage has been shown and discussions have been focused on the e¡ect of noise-related free oxygen radicals in cochlear damage. It has been reported that the increase in free oxygen radical formation and activity may lead to damage in cochlear sensory epithelium resulting in change of hearing threshold (Seidman et al., 1993 ; Liu, 1992). This study was performed to investigate the relationship between noise-related hearing impairment of industrial workers being exposed to long-term continuous noise and free oxygen radicals.
0378-5955 / 01 / $ ^ see front matter ß 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 5 9 5 5 ( 0 1 ) 0 0 3 6 5 - 3
HEARES 3763 5-11-01
44
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
2. Materials and method The present study was performed on a total of 60 patients, at F|rat Medical Centre ENT Clinic, F|rat University. The design of this study has been approved by the Ethical Committee of the F|rat University. 2.1. Experimental group This study consisted of 75 male workers employed in the noisy units of a hydroelectric power plant. In anamnesis, they were asked whether they had a current or past hearing disorder. None of the subjects had any known pathologies at the time of the experiment. Meanwhile, smokers and alcohol users were avoided. Fifteen workers were excluded because they did not meet the study criterions. To determine the hearing thresholds at 250, 500, 1000, 2000, 4000, 6000 and 8000 Hz, a standard ascending/descending method was applied to the 60 workers who had no hearing disorder, no pathology in otoscopic examination and having a normal tympanometry. To avoid the possible e¡ect of temporary threshold shift on permanent threshold shift, all tests were performed after at least 18 h of noise-free period (Yellin, 1991). The experimental group was divided into three subgroups according to the areas that the workers were employed in. 2.2. Group I (turbine group) Consisted of 20 workers who worked without protection for 8 h a day in the turbine part of the hydroelectric power plant where there is a continuous noise level of 95^110 dB. 2.3. Group II (machinery maintenance workshop group) Consisted of 20 workers who worked without protection for 8 h a day in the generator room or machine room of the hydroelectric power plant where the continuous noise level was 75^85 dB. 2.4. Group III (outdoor experimental group) Consisted of 20 workers who worked in the open areas of the hydroelectric power plant where the continuous noise level was below 75 dB. 2.5. Control group Consisted of 20 male volunteers employed in the Medical Centre where the study was conducted. The inclusion criterions were: no pathology in otoscopic examinations, having a normal tympanometry and a
normal hearing threshold at all frequencies between 250 and 8000 Hz indicated in audiograms. 2.6. Audiologic tests They were carried out in standard acoustically controlled rooms (Industrial Acoustics Company) using Interacoustics Clinical Computer Audiometer Model AC5, Interacoustics Impedance Audiometer AZ7 and Interacoustics XYT Recorder Model AG3, (Interacoustics, Assens, Denmark). The audiometer was calibrated by a Bruel-Kjaer Type 4144 microphone, Type 1613 audio frequency spectrometer and 6 cc arti¢cial ear plug. Noise levels in di¡erent units of the hydroelectric power plant were measured using a noise meter (Bruel Kjaer 2235, Copenhagen, Denmark). 2.7. Biochemical assessments Blood samples (10 ml) were taken under sterile conditions in tubes with ethylenediaminetetraacetic acid from each of the subjects in the experimental and control groups. Samples were centrifuged at 3000 rpm for 10 min and the plasma was used to measure malondialdehyde (MDA) levels, and erythrocytes were used to measure glutathione peroxidase (GSH-Px) activity. MDA was measured by a spectrophotometer (Schimadzu UV-1201 Spectrophotometer, Schimadzu Corp., Japan) using a method modi¢ed from Satoh (1978) and Yagi (1984) ; GSH-Px activity was measured using the method of Paglia and Valentine (1967) based on the oxidation of NADPH by glutathione reductase enzyme. 2.8. Statistical analysis One-way variance analysis and Tukey's HSD test were used. 3. Results The mean age of 60 workers working in the noise parts of the hydroelectric power plant for 14.21 þ 6.11 years was 28^49 years (37.7 þ 5.6) and the age range of the control group was 28^48 (mean 36.8 þ 4.5). The audiometric data including the hearing thresholds in dB nHL of the control and experiment groups at seven di¡erent frequencies between 250 and 8000 Hz, and their statistical comparison is shown in Table 1. Mean pure tone audiometric thresholds in group I and II with noise-induced hearing loss were signi¢cantly higher than in those of group III and control subjects at octave frequencies in the range of 2^8 kHz. Hearing
HEARES 3763 5-11-01
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
45
Table 1 Hearing threshold averages, standard deviations and statistical comparison of the experiment and control groups Test frequency (Hz)
Group I
Group II
Group III
Control
250 500 1000 2000* 4000* 6000* 8000*
13.5 þ 4.1 12.9 þ 5.6 13.4 þ 4.8 20.6 þ 9.0# 25.6 þ 12.2# 37.6 þ 15.49 30.2 þ 18.19
11.9 þ 6.3 13.4 þ 8.4 13.5 þ 7.7 18.0 þ 8.6i 19.5 þ 9.8i 26.1 þ 10.2i 20.5 þ 11.3
11.5 þ 3.8 11.1 þ 4.9 11.2 þ 4.5 12.6 þ 6.1 13.8 þ 5.9 15.5 þ 4.2 14.1 þ 11.2
8.1 þ 4.7 9.3 þ 5.5 9.9 þ 7.8 10.2 þ 5.6 11.3 þ 8.8 14.5 þ 6.2 13.5 þ 7.6
*P 6 0.0001 (one-way analysis of variance); #P 6 0.05 (Tukey's HSD test), compared group I with control and group III; iP 6 0.05 (Tukey's HSD test), compared group II with control and group III; 9P 6 0.05 (Tukey's HSD test), compared group I with control, group II and group III.
losses were more evident at 6 kHz than at 2, 4 and 8 kHz. The level of MDA and GSH-Px of the control and the experimental groups with associated statistical comparison is summarized in Table 2. MDA levels were higher in the experimental groups versus the control group. MDA levels of the experimental groups increased, but only the MDA level of group I was signi¢cantly di¡erent from the other groups (P 6 0.05). GSHPx activity was the highest in group I. It was signi¢cantly di¡erent in groups I and II versus the control group and group III. The di¡erence was also signi¢cant when comparison was made between group I and II (P 6 0.05). 4. Discussion With the exception of presbycusis, the most common reason of sensorineural hearing impairment is noise (Dobie, 1995). It has been known for many years that high levels of noise cause permanent damage to the hearing mechanism. The adverse a¡ect of noise on hearing depends on the degeneration and damage of internal hair cells in the basal coil of the Corti organ. The audiological indicator of it is the bilateral, symmetric, sensorineural type hearing impairment seen around 3^6 kHz (Ward, 1991). The severity, frequency, duration and temporal characteristics (continuous, £uctuating, intermittent) of the noise are important factors affecting the cochlear damage (Attias and Pratt, 1985 ; Osguthorpe and Klein, 1991).
Although each individual is di¡erently a¡ected by the noise, there are several other important factors. The ¢rst one is the period during which the person works continuously and the second one is being in the same environment for years. Being exposed to 100 dB of noise every day for a continuous period of 8 h initially results in a hearing impairment progressing fast around 4 kHz, but at frequencies under 4 kHz, no substantial change occurs. People working in noise environments have an impairment of 15^20 dB in the ¢rst 1^2 years and this level gradually increases in the ¢rst 10 years. Then, it slows or completely stops (Alberti, 1997). C°elik et al. (1996) have reported 1^8 kHz hearing impairment in the workers who have been exposed to 95^110 dB vocational noise for 1^20 years and has emphasized that hearing impairment was particularly obvious at 4^6 kHz. They have also noted that hearing impairment is highest in the ¢rst 10 years and then it begins to decrease. Seidman et al. (1993) have stated that free oxygen radicals are responsible for the noise-related damage in sensory epithelium and the damage might be prevented by using radical scavengers. In a study to investigate the noise-related free radical formation in cochlea, it was found a that superoxide anion radical was formed in the luminal membranes of stria vascularis of the marginal cells of guinea pigs which have been exposed to 120^125 dB of noise for 3 h (Yamene et al., 1995). This was believed to be the result of the increase in free radicals due to the ischemia-reperfusion occurring in the cochlear microcirculation because of the noise.
Table 2 MDA (nmol/ml) and GSH-Px (U/mgHb) averages, standard deviations and statistical comparisons of the control and experiment groups MDA GSH-Px
Group I
Group II
Group III
Control
0.54 þ 3.1*8 5.85 þ 1.1*v
0.39 þ 2.1* 5.18 þ 1.5*i
0.36 þ 1.8* 4.43 þ 1.1*
0.31 þ 2.3* 4.09 þ 2.3*
*P 6 0.0001 (one-way analysis of variance), 8 P 6 0.05 (Tukey's HSD test), compared group I, group II and group III with control; v P 6 0.05 (Tukey's HSD test), compared group I, group II and group III with control; i P 6 0.05 (Tukey's HSD test), compared group II and group III with control.
HEARES 3763 5-11-01
46
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
Herken et al. (2001) studied schizophrenic patients, whereas Licastro et al. (2001) and Mihailovic et al. (1998) examined patients with Alzheimer and chronic heart failure, respectively. They measured the level of activity of GSH-Px in peripheral blood and determined a correlation between the level of GSH-Px and these diseases. The method used in the present study and the results were well correlated with the literature in this aspect. Ising (2000) reported that noise caused an increase in the level of acute and chronic hormones and consequently, elevated levels of free oxygen radicals were observed. Similarly, it was shown that the level of these oxidant agents can also be measured in several other organs, i.e. liver. Salvi et al. (2001), reported detonation of enzymatic activity, biological function loss in protein transport and in receptors and determined the structural damages of proteins due to free radicals. Additionally, it was concluded that this structural damage can be prevented using antioxidant agents. Ohinata et al. (2000) investigated the noise-related hearing impairment and determined the correlation between auditory damage and reactive oxygen species. 8Isoprostan was studied biochemically and histochemically as a predictor of free oxygen radicals. It was reported that the level of 8-isoprostan increased in respect to the duration of the noise time. 8-Isoprostan levels were found to be increased in the organ of Corti, spiral ganglion cells and stria vascularis. With these data, they reported that free oxygen radicals played a role in the development of noise-associated auditory damage and determined the correlation between lipid peroxidation and noise-related damage in the organ of Corti. Although MDA is not a speci¢c or quantitative indicator of fatty acid oxidation, it has correlation with the level of lipid peroxidation. MDA accumulation, which is related to lipid peroxidation, is an important component of the damage that develops in the reperfusion phase (Halliwell, 1994). Liu (1992) has evaluated the changes in MDA levels of the cochlear tissue and auditory brainstem response hearing threshold in guinea pigs in order to investigate the role of free oxygen radicals in hearing impairment due to blast trauma. He has reported that in the ¢rst hours after blast trauma, MDA levels of the cochlea tissue begin to increase; MDA level is at peak on the 3rd and 6th days. Although it reaches to normal level on the 8th day, it reaches to a second peak on the 12th day, and hearing thresholds are proportional to MDA level. Based on these ¢ndings, it has been argued that hearing impairment related to blast trauma stems from the increase in free oxygen radicals reactions. The results of our study also support this conclusion that MDA levels increase proportionally with the increased level of noise-related hearing impairment.
Cells have antioxidant defence mechanisms that prevent, limit or partly repair oxidative damage. The most e¡ective defence mechanism is the enzyme systems. One of them is the GSH-Px enzyme which reduces the hydroxy peroxides to water at the expense of reduced glutathione. GSH-Px prevents the e¡ect of free radicals and protects the cell from damage (Halliwell, 1994). In an experimental study, Yamasoba et al. (1998) have discussed that noise increases the glutathione level in the lateral wall of the cochlea, and it does not change in modiolus or sensory epithelium. Accordingly, noise increases the selective glutathione synthesis in the lateral wall of the cochlea. Jacono et al. (1998) have reported that hair cell damage in the Corti organ decreases proportionally with the increase in glutathione levels and catalase levels in stria vascularis, and suggested that the glutathione enzyme system is a protective mechanism against the noise-related hearing impairment. In our study, we have also found that GSH-Px activity increases proportionally with the increased level of noise-related hearing impairment, although there is no statistically signi¢cant di¡erence between group III and the control group. It has been pointed out in many studies that, there is a role of the increased free radical formation to the cochlear damage during high-level noise. On the other hand, Ising and Braun (2000) have studied the e¡ects of acute and chronic noise on the endocrine system. Henry and Stephens (1977) have made a model for psychophysiological stress of noise. They have pointed out that three di¡erent reactions occurred in their experiment; (1) an increase of adrenaline and noradrenaline in suprarenal medulla in ¢ght^¢ght reaction, (2) hypothalamic pituitary adrenocortical system was inhibited and cortisol was increased within defeat reaction, (3) the expression of noradrenaline of sympathetic synapses was increased in workers supplied with noise higher than 90 dB in their environment. In this study, they have mentioned that stress hormones are increased in the blood by noise and the important e¡ect of chronic noise found in the unprotected workers is hypercortisolism. In our study, we have also noticed that noise is a very important stress factor and the activity of blood MDA and GSH-Px is increased in those people working in high-noise environments. In the same worker group, hearing defects were found especially at 6 kHz. Because noise-related hearing impairment can not be treated medically or by surgery, the main aim is to prevent cochlear damage caused by noise and to protect hearing ability. We have found that MDA and GSH-Px activity values increase progressively with the severity of noise, and with these changes the physiological protection mechanisms are e¡ective to a certain degree, however, that is not su¤cient. In conclusion, we suggest that the existing natural antioxidants in the cell are not
HEARES 3763 5-11-01
I. Kaygusuz et al. / Hearing Research 162 (2001) 43^47
enough to prevent the noise-related damage and cochlear damage can be minimized by prescribing antioxidant drugs to those who work in noise environments. However, more data are needed at the biochemical and epidemiologic levels for a better understanding of these ¢ndings. References Alberti, P.W., 1997. Noise and the ear. In: Kerr, A.G., Dafyold, S., (Eds.), Scott-Brown's Otolaryngology. Reed Educational and Professional Publishing Ltd, Oxford, pp. 1^31. Attias, J., Pratt, H., 1985. Auditory evoked potential correlates of susceptibilty to noise induced hearing loss. Audiology 24, 149^156. ë ztu«rk, A., 1996. Hearing parameters in noise C°elik, O., Yalc°|n, S°., O exposed industrial workers. Auris Nasus Larynx 23, 127^132. Dobie, R.A., 1995. Prevention of noise-induced hearing loss. Arch. Otolaryngol. Head Neck Surg. 121, 385^391. Halliwell, B., 1994. Free radicals, antioxidants, and human disease: curiosity, cause, or consequence? Lancet 344, 721^724. Hawkins, J.E., 1971. The role of vasoconstriction in noise-induced hearing loss. Ann. Otol. Rhinol. Laryngol. 80, 903^913. Henry, J.P., Stephens, P.M., 1977. The social environment and essential hypertension in mice; possible role of the innervation of the adrenal cortex. Prog. Brain Res. 47, 263^267. Herken, H., Uz, E., Ozyurt, H., Sogut, S., Virit, O., Akyol, O., 2001. Evidence that the activities of erythrocyte free radical scavenging enzymes and the products of lipid peroxidation are increased in di¡erent forms of schizophrenia. Mol. Psychiatr. 6, 66^73. Ising, H., 2000. Acute and chronic stress hormone increases in noise exposure. Schr.reihe Ver. Wasser Boden Lufthyg. 106, 169^177. Ising, H., Braun, C., 2000. Acute and chronic endocrine e¡ects of noise: review of the research conducted at the Institute for Water, Soil and Air Hygiene. Noise Health 7, 7^24. Jacono, A.A., Hu, B., Kopke, R.D., Henderson, D., Van De Wetar, T.R., Steinman, H.M., 1998. Changes in cochlear antioxidant enzyme activity after sound conditioning and noise exposure in the chinchilla. Hear. Res. 117, 31^38. Licastro, F., Pedrini, S., Davis, L.J., Caputo, L., Tagliabue, J., Savorani, G., Cucinotta, D., Annoni, G., 2001. Alpha-1-antichymotrypsin and oxidative stress in the peripheral blood from patients with probable Alzheimer disease: a short-term longitudinal study. Alzheimer Dis. Assoc. Disord. 15, 51^55.
47
Liu, Z., 1992. Experimental study on the mechanism of free radical in blast trauma induced hearing loss. Zhonghua Er Bi Yan Hou Ke Za Zhi 27, 24^26. Mihailovic, M.B., Avramovic, D.M., Jovanovic, I.B., Pesut, O.J., Matic, D.P., Stojanov, V.J., 1998. Blood and plasma selenium levels and GSH-Px activities in patients with arterial hypertension and chronic heart disease. J. Environ. Pathol. Toxicol. Oncol. 17, 285^289. Nakai, Y., Masutani, H., 1988. Noise induced vasoconstriction in the cochlea. Acta. Otolarngol. 447 (Suppl.), 23^27. Ohinata, Y., Miller, J.M., Altschuler, R.A., Schacht, J., 2000. Intense noise induces formation of vasoactive lipid peroxidation products in the cochlea. Brain Res. 878, 163^173. Osguthorpe, J.D., Klein, A.J., 1991. Occupational hearing conservation. Otolaryngol. Clin. N. Am. 24, 403^414. Paglia, D.E., Valentine, W.N., 1967. Studies on the quantitative and qualitative characterization of erythtrocyte glutatione peroxidase. J. Lab. Clin. Med. 70, 158^169. Salvi, A., Carrupt, P.A., Tillement, J.P., Testa, B., 2001. Structural damage to proteins caused by free radicals: asessment, protection by antioxidants, and in£uence of protein binding. Biochem. Pharmacol. 61, 1237^1242. Satoh, K., 1978. Serum lipid peroxide in cerebrovascular disorders determined by a new colorimetric method. Clin. Chim. Acta 90, 37^43. Seidman, M.D., Sh|vapuja, B.G., Quirk, W.S., 1993. The protective e¡ects of allopurinol and superoxide dismutase on noise-induced cochlear damage. Otolaryngol. Head Neck Surg. 109, 1052^1056. Ward, W.D., 1991. Noise induced hearing damage. In: Paparella, M.M., Shumrick, D.A., Gluckman, J.L., Meyerho¡, W.L., (Eds.), Otolaryngology. WB Saunders Co., London, pp. 1639^ 1652. Yagi, K., 1984. Assay of lipid peroxidation in blood plasma or serum. Methods Enzymol. 105, 328^363. Yamasoba, T., Harris, C., Schoji, F., Lee, R.J., Nuttall, A.L., Miller, J.M., 1998. In£uence of intense sound exposure on glutathione synthesis in the cochlea. Brain Res. 804, 72^78. Yamene, H., Nakai, Y., Takayama, M., Konishi, K., Iguichi, H., Nakagawa, T., Shibata, S., Kato, A., Sunami, K., Kawakatsu, C., 1995. The emergence of free radicals after acoustic trauma and strial blood £ow. Acta. Otolaryngol. Stockholm 519 (Suppl.), 87^97. Yellin, M.W., 1991. Hearing measurment in adults. In: Paparella, M.M., Shumrick, D.A., Gluckman, J.L., Meyerho¡, W.L., (Eds.), Otolaryngology. WB Saunders Co., London, pp. 961^ 975.
HEARES 3763 5-11-01