engleski

Application Of Different Cytogenetic Endpoints In Risk Assessment Of Occupationally Exposure To Ultrasound

Ultrasound as a nonionizing form of energy is usable in many sensitive circumstances where X-rays might be damaging. Because ultrasonography is an invasive procedure, theoretical risks to the tissues do exist ; however, there are no known examples of tissue damage from conventional ultrasound imaging. Reports about potentially harmful effects of diagnostic ultrasound on human chromosomes are contradictory. In present study the cytogenetic damage resulting from occupationally exposure to ultrasound was investigated. In order to investigate possible DNA damaging effects of ultrasonic waves on human genome different cytogenetic endpoints: chromosome aberrations (CA), sister chromatid exchanges (SCE) and micronucleus assay (MN) combined with Giemsa, DAPI and silver staining techniques were employed. The subjects of study were medical staff daily occupationally exposed to pulsed wave color Doppler ultrasound in frequency2.5-7.5 MHz (absolute max. ultrasonic power 0.8-4.9 mW/cm2, absolute max. spatial peak-pulse average intensity 60-110 W/cm2, absolute max. spatial peak-temporal average intensity 1.9-20 mW/cm2) and control subjects. Samples of peripheral blood were cultivated in vitro for 48 respectively 72 hours on F-10 medium. For the SCE analysis in medium was added 10 � Ýg/ml of 5-bromodeoxyuridine. To obtain cytokinesis-blocked lymphocytes 6 � Ýg/ml of cytochalasin-B was added in medium. Presence of structural chromosome aberrations was evaluated by scoring of 200 well-spread metaphases per subject. To determine frequency and distribution of micronuclei for each staining technique 500 binucleated cells per subject were scored. For determination of SCE 50 cells per subject were analysed. Results of cytogenetic endpoints indicate higher level of genome damage in somatic cells of exposed subjects compared to control. The percentage of cells with CA in the exposed group was increased compared with control group. Predominantly detected CA were chromatid breaks and acentric fragments. Frequency of SCE in exposed group was 5.75 and range of SCE 2-12, and was increased compared to control (frequency of SCE 3.02, range 0-7). We also observed increase in the total number of micronuclei and changes in their distribution in exposed subjects compared to control. Staining with DAPI and silver nitrate was used to distinguish micronuclei originating from breakage or mitotic loss of certain human chromosomes bearing DAPI-positively or silver-positively stained regions. Based on different intensity of DAPI staining signal-positive and signal-negative micronuclei were noticed, while silver staining has revealed AgNOR+ and AgNOR- micronuclei. In exposed subjects a prevalence in number of AgNOR+ over AgNOR- micronuclei compared to control was observed, indicating greater susceptibility of chromosomes from D and G groups to damage caused by continous occupationally exposure to ultrasound. In spite of their limitations, our results indicate that combination of conventional Giemsa staining of micronuclei with fluorescent dye DAPI and silver nitrate can be valuable complement to the standard micronucleus assay. However, further investigations are necessary to clarify effects of ultrasound exposure on health risks, especially on DNA damages.

ultrasound; chromosome aberrations; sister chromatid exchanges; micronucleus assay; Giemsa; DAPI; silver staining

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