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Hearing loss can occur in newborns exposed to high-level noise; noise exposure can cause more physiological stress and can lead to DNA damage. This study was designed to determine DNA damage in newborn rats exposed to sound at different concentrations. For this purpose, 28 newborn (3-6 days old) rats were divided into four groups of 7 rats in each group (Control and Groups of 40 decibel (dB), 70 dB, and 110 dB]. In the experimental groups, 40 dB, 70 dB, and 110 dB (7.5-15 kHz) of sound was applied to the experimental groups for 30 min a day for 7 days. DNA damage levels in the serums obtained from this study were determined by the enzyme-linked immunosorbent assay (ELISA) method. According to this, it was determined that DNA damage in the group exposed to 110 dB showed a statistically significant increase (P < 0.05) compared to the compared to the control, 40 dB, and 70 dB groups. Related to the subject, it was concluded that DNA damage may occur in newborns exposed to 110 dB or higher sound in neonatal units, wards, and home environments with newborn babies. Mothers should be warned about this situation and noise should be kept under 110 dB volume in the environments with the newborns.
People are exposed to noise from sources such as the environment, traffic, housework, and music in their daily lives. Sound is expressed as decibels (dB) in the algorithmic scale. Sounds above 20 kHz are called ultrasonic sound. While humans are able to hear sound waves between 16 Hz and 20 kHz, rats can hear sounds between 250 Hz and 80 kHz (Etzel et al.; Soylu).[1,2] Noise can lead to many health problems, such as hearing loss, sleep disorders, and failure in cognitive activations. In addition, it may lead to reduction of social activations by making the individual aggressive. It can lead to coronary heart diseases, high blood pressure, headache, anxiety, nausea, and severe physiological problems. Rates of incidence of high blood pressure, cardiovascular disease, and cancer are said to be higher in people living in areas close to the airports (Demirel et al.).
It is reported that people in Europe are exposed to environmental noise generated by sound higher than 65 dB. Just as exposure to much noise causes physiological stress, there are also studies indicating that it can cause DNA damage, as well (Etzel et al.; Meek et al.; Frenzilli et al.; Sarkaki and Karami; Soylu).[1,2,4,5,6] Etzel et al. reported that hearing loss may occur in newborns being exposed to high noise, development may slow down in the intrauterine period, and noise may be associated with premature births.
All changes in genetic material caused by the effect of endogenous or exogenous factors are called “DNA damage” (Turner et al.; Kulaksız and Sancar; Onur et al.[7,8,9] 8-hydroxy-2’-deoxyguanosine (8-OH-dG) is the most widely known biomarker of oxidative DNA damage. Increase in the amount of 8-OHdG may occur depending on many pathological conditions, including cancer, diabetes, and hypertension, besides aging (Kasai; Loft et al.; Cooke et al.; Lee et al.; Shen et al.).[10,11,12,13,14] Oxidative stress is known to cause damage as a result of a number of lesions such as base and sugar modifications on DNA by different mechanisms, single- and double-strand breakages, abasic regions, and DNA-protein cross-linking (Williams and Jeffrey; Cooke et al.; Turner et al.).[7,12,15]
This study was designed to determine 8-OHdG levels, which is the indicator of oxidative damage in order to determine DNA damage in newborn rats being exposed to sound at different concentrations [40.70 Db and 110 dB (7.5-15 kHz)].
In this study, newborn rats obtained from Yuzuncu Yil University, the Experimental Research Unit were used. The ear canals of rats open when they reach the age of 2.5-3.5 days (Soylu). Thus, 28 newborn rats (4-6 days old) and their mothers were used. Rats were divided into two groups including the noise group (3 different doşes — 21 rats) and the control group (7 rats). The rats in both groups were kept under the same physical conditions without being separated from their mothers until the end of the study. Mothers were fed with standard rat feed and tap water ad libitum.
The rats in the group that would be exposed to sound was divided into three groups in itself and were exposed to sound at the intensity of 40 dB, 70 dB, and 110 dB (7.5-15 kHz) for 30 min daily for 7 days (Hughes and Bardon 1981, Etzel et al.). Exposure to the sound was performed using a specially designed glass bulb with the dimensions of 120×60×80 cm3 placed in a room with proper physical conditions. Holes were opened in the jar lid of the bulb that would help the animals to get fresh air. Computer speakers were used for the exposure of the sound, and the decibel of the sound given was measured with the Smart Sensor AR844 digital sound level meter (Shenzhen Graigar Technology Co. Ltd., Shenzhen, China). After the operation is continued for 7 days, animals were sacrificed by anesthesia with ketamine at the dose of 75-90 mg/kg with the exsanguination method. The blood taken was centrifuged at 3000 rpm for 10 min and the serums were separated. For the determination of serum 8-OHdG levels, it was measured 450 nm absorbance (Biochrom Anthos Zenyth 200 rt microplate reader, Cambridge, England) by using DNA damage ELISA kit (ADI-EKS-350 from Enzo Life Science, Farmingdale, NY, USA). Statistical results of the study were calculated using SPSS 10.0 (SPSS Inc., Chicago, IL, USA) software package. Contemplated properties were expressed as descriptive statistics, median, mean, standard deviation, and minimum and maximum values. The Kruskal-Wallis test was used to compare the groups in these features, and Dunn's test was used to identify different groups.
The study results are presented in Table 1 below.
The statistical significance of A compared to B, which is at the same column, was P < 0.05.
It was determined that the data obtained from the groups to which 40 dB and 70 dB were applied were statistically insignificantly different (P > 0.05) compared to the control group and to each other.
It was also determined that 8-OHdG levels of the group to which 110 dB was applied increased at a statistically significant rate (P < 0.05) compared to the control group and the data of the 40 dB and 70 dB groups.
Noise stress may also cause some psychosomatic and physiological problems as well as problems in the nervous system. It may lead to low birth weight of the newborns, stillbirths, and teratogens and abortions of the fetus. Thus, noise is one of the most important environmental factors for pregnant women and fetuses. It is stated that exposure to noise during pregnancy causes the detrimental effect of the brain development after birth, damage on the cognitive functions, even changes in the myocardium and DNA damage, along with physiologic stress (Meek et al.; Frenzilli et al.; Sarkaki and Karami).[4,5,6] It is expressed that noise affects the neurotransmitter systems and corticotrophin-releasing factor (CRF) in rats exposed to prenatal stress increases substantially (Sarkaki and Karami).
Nuclear and mitochondrial DNA is a common target of oxidative damage. Guanine is the most nucleic acid base prone to oxidation, which adds a hydroxyl group to the eighth position of the guanine molecule (Nishikawa et al., 2003). DNA is continuously exposed to oxidative damage from exogenous origin and endogenous oxidants. Thus, all kinds of factors that can lead to oxidative damage can cause DNA damage and thus 8-OHdG formation (Kasai; Lee et al.; Shen et al., 2007).[10,13,14]
There are experimental studies on the physiological effects of noise and the identification of metabolic responses in parallel with this. Hence, Kim et al. separated pregnant rats into two groups and had one group listen to the noise and the other group to the music. They detected that there were decreases in the motor cortex and somatosensory cortical thicknesses and in the neurogenesis of the offspring of rats exposed to the noise, while in contrast, these values increased in those exposed to the music, and they provided evidences for neurological impact related to the noise.
In studies on the effects of the noise on DNA damage formation, DNA damage was revealed on the rats exposed to 120 dB noise for 8 h, 72 h, and 672 h. Accordingly, the first 8 h of noise exposure are reported to be a critical period for antioxidant therapy (Van Campen et al.). Lenz et al., (2003), in a a study conducted on the rats, showed that DNA damage in the heart muscle in the 24th hour showed a statistically significant increase in the group exposed to the sound compared to the control group after exposing the animals to sound up to 100 dB for 12 h with an electronic sound meter with a speaker placed in two corners at 40 cm distance in the cages.
In the present study, in accordance with the literature data, it was determined that DNA damage in the group exposed to 110 dB sound showed statistically significant increase after 7 days (P < 0.05) compared to the control, 40 dB, and 70 dB groups. Clerici and Yang reported that DNA damage was higher in rats exposed to sound for a long period. In this study, despite the implementation of relatively high 40 dB and 70 dB, it was determined that the change in the level of DNA damage was statistically insignificant (P > 0.05) compared to each other and the control group. This situation is thought to have been caused by the shorter duration of exposure to the sound.
As a result, it was concluded that DNA damage occurred in newborn rats exposed to 110 dB or higher sound, which is a situation that should be considered for humans, and that mothers should be warned about this situation: Newborns should not be exposed to high volumes for a long time. The results obtained in this study are considered to be a step toward further studies detailed with different parameters on the detection and prevention of DNA damage induced by noise at different intensities and durations.
There are no conflicts of interest.