Identification by microscopically controlled comet assay of peritoneal macrophages in a mixture of peritoneal exudate for DNA strand break analysis

Genotoxic effects of 1064-nm Nd:YAG and 532-nm KTP lasers on fibroblast cell cultures

BACKGROUND

Several different laser types are used in cutaneous surgery. The neodymium:yttrium-aluminium-garnet (Nd:YAG) and frequency-doubled Nd:YAG (KTP, potassium titanyl phosphate) lasers are widely used in dermatology.

OBJECTIVES

To investigate the possible genotoxic effects on fibroblasts of irradiation with a 1064-nm Nd:YAG laser and a 532-nm KTP laser.

METHODS

Fibroblast cell cultures were exposed to each of the lasers, using 10-mm spot size at 60 ms pulse duration with 10, 20, 40 J/cm(2) and 3, 6, 12 J/cm(2) fluences, respectively. Fibroblasts in passages 1-6 were used. During laser irradiation, 96-well microplate cultures were kept on a cooling block and transported on ice and in the dark, and processed immediately for single-cell gel electrophoresis (SCGE) assay (also known as a comet assay).

RESULTS

DNA damage was determined by computerized assessment of comet assay. There was increasing damage with increasing numbers of passages. For the Nd:YAG laser, the greatest damage occurred on passages 5 and 6, whereas the greatest damage appeared at passages 3 and 4 for KTP and returned to baseline at passages 5 and 6. Damage also increased with each dose increment for both wavelengths. At the highest dose for both wavelengths (Nd:YAG 40 J/cm(2) and KTP 12 J/cm(2)), damage was higher with the Nd:YAG laser.

CONCLUSIONS

Different patterns of cellular damage were seen for different cell-culture passages, treatment doses, and laser wavelengths. These dose ranges are generally used for the treatment of vascular and pigmented lesions and for rejuvenation purposes. As replicative ageing or cell senescence is one of the critical factors determining the extent of cell damage induced by laser therapy, these results may have important implications for clinical practice.

Ultrasound increases DNA damage attributable to cisplatin in cisplatin-resistant human ovarian cancer cells

OBJECTIVE

An increased capacity for DNA repair plays a very important role in cisplatin (DDP) resistance in ovarian cancers. Ultrasound is a potential chemotherapy sensitizer. The aim of this study was to determine whether ultrasound in conjunction with chemotherapy increases DNA damage in chemoresistant human ovarian cancer cells.

METHODS

Ultrasound and/or cyclosporin A were used to overcome chemoresistance in a DDP-resistant human ovarian cancer cell line, COC1/DDP. DNA damage was quantified by comet assay, a form of single-cell gel electrophoresis in which the length of the comet tail reflects the level of DNA damage.

RESULTS

Neither ultrasound nor cyclosporin A alone led to detectable DNA breakage. The use of ultrasound increased DNA breakage due to DDP, while the use of cyclosporin A did not. The addition of ultrasound and cyclosporin A in conjunction with DDP resulted in a 2.55 times increase in the length of comet tail compared with using DDP alone, while their combined use resulted in a 1.73 times increase compared with the combination of just DDP and insonation.

CONCLUSIONS

Insonation increases DNA breakage attributable to DDP in chemoresistant human ovarian cancer cells, and might sensitize cyclosporin A.

Radiation-induced apoptosis in peritoneal resident macrophages of C3H mice

Gamma ray-radiation induced significant apoptosis in peritoneal resident macrophages (PRMs) of C3H/HeJ (C3H) mice, but not in other strains of mice. To investigate the role of DNA damage in the apoptosis, DNA damage was quantified in PRMs by use of the alkaline single-cell gel electrophoresis (Comet) assay. No significant difference was found between C3H and C57Black/6 mice in either radiation-induced DNA damage or repair. Radiation induced apoptosis at the same levels in PRMs of p53 knockout mice and atm knockout mice as those of wild-type C3H mice; however radiation-induced apoptosis was significantly less extensive in the thymocytes of these mutant mice than in those of wild-type mice. Apoptosis was also induced at the same level by an irradiation in PRMs of C3H scid mice as in those of wild-type C3H mice. Therefore it was suggested that radiation-induced DNA damage and TP53, ATM, or DNA-PK-mediated cellular responses occurring downstream thereof were not involved in the radiation-induced apoptotic cell death in C3H mouse PRMs.

Detection of radiation-induced apoptosis using the comet assay

The electrophoresis pattern of apoptotic cells detected by the comet assay has a characteristic small head and spread tail. This image has been referred to as an apoptotic comet, but it has not been previously proven to be apoptotic cells by any direct method. In order to identify this image obtained by the comet assay as corresponding to an apoptotic cell, the frequency of appearance of apoptosis was examined using CHO-K1 and L5178Y cells which were exposed to gamma irradiation. As a method for detecting apoptosis, the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay was used. When the frequency of appearance of apoptotic cells following gamma irradiation was observed over a period of time, there was a significant increase in appearance of apoptosis when using the TUNEL assay. However, there was only a slight increase when using the comet assay. In order to verify the low frequency of appearance of apoptosis when using the comet assay, we attempted to use the TUNEL assay to stain the apoptotic comets detected in the comet assay. The apoptotic comets were TUNEL positive and the normal comets were TUNEL negative. This indicates that the apoptotic comets were formed from DNA fragments with 3'-hydroxy ends that are generated as cells undergo apoptosis. Therefore, it was understood that the characteristic pattern of apoptotic comets detected by the comet assay corresponds to cells undergoing apoptosis.

Comet assay measurements of DNA damage in cells by laser microbeams and trapping beams with wavelengths spanning a range of 308 nm to 1064 nm

DNA damage induced in NC37 lymphoblasts by optical tweezers with a continuous-wave Ti:sapphire laser and a continuous-wave Nd:YAG laser (60-240 mW; 10-50 TJ/m2; 30-120 s irradiation) was studied with the comet assay, a single-cell technique used to detect DNA fragmentation in genomes. Over the wavelength range of 750-1064 nm, the amount of damage in DNA peaks at around 760 nm, with the fraction of DNA damage within the range of 750-780 nm being a factor of two larger than the fraction of DNA damage within the range of 800-1064 nm. The variation in DNA damage was not significant over the range of 800-1064 nm. When the logarithm of damage thresholds measured in the present work, as well as values reported previously in the UV range, was plotted as a function of wavelength, a dramatic wavelength dependence became apparent. The damage threshold values can be fitted on two straight lines, one for continuous-wave sources and the other for pulsed sources, irrespective of the type of source used (e.g. classical lamp or laser). The damage threshold around 760 nm falls on the line extrapolated from values for UV-radiation-induced damage, while the data for 800-1064 nm fall on a line that has a different slope. The change in the slope between 320 and 340 nm observed earlier is consistent with a well-known change in DNA-damaging mechanisms. The change observed around 780 nm is therefore suggestive of a further change in the mechanism(s). The data from this work together with our previous measurements provide, to the best of our knowledge, the most comprehensive view available of the DNA damage produced by microfocused light.