title: Some causes of inter-laboratory variation in the results of comet assay.
abstract: We performed an inter-laboratory study to determine the variation of comet assay results and to identify its possible reasons. An exchange of slides between Labs in different stages of the comet assay protocol was performed. Because identical slides, durations of alkali treatment and electrophoresis, and similar electric field strengths (2.0 V/cm and 2.14 V/cm) were used, we concluded that the observed inter-laboratory difference in the results is directly associated with the electrophoresis step. In Lab 1, mouse bone marrow cells were exposed to methyl methanesulfonate at concentrations of 10, 25 and 50 μM for 3 h at 37 °C. In Lab 2, cells the same as in Lab 1 were immobilized in LMA on slides and exposed to X-rays at doses of 3-8 Gy. We found that the transportation of slides after lysis or electrophoresis step, as well as different dyes used for scoring did not produce any significant effect on the results. No substantial difference in the data was also revealed when various software packages were used for image analysis. The temperature of the alkaline solution was shown to increase during electrophoresis and, besides, the temperature heterogeneity of the solution took place in the area of the platform, with a maximum in the middle of the chamber. The temperature heterogeneity could affect the rate of conversion of alkali labile sites into single stranded breaks. Thus, it was clearly indicated that real temperature variations during the alkali treatment and electrophoresis were an essential factor in the variability of the results between our Labs.
authors.affiliation: Institute of Theoretical and Experimental Biophysics of Russian Academy of Sciences, Pushchino, Russia. Electronic address: sirota@iteb.ru.
authors.forename: Nikolai P
authors.initials: NP
authors.lastname: Sirota
authors.affiliation: Zakusov Research Institute of Pharmacology of RAMS, Moscow, Russia.
authors.forename: Aliy K
authors.initials: AK
authors.lastname: Zhanataev
authors.affiliation: Institute of Theoretical and Experimental Biophysics of Russian Academy of Sciences, Pushchino, Russia.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Kuznetsova
authors.affiliation: Institute of Theoretical and Experimental Biophysics of Russian Academy of Sciences, Pushchino, Russia.
authors.forename: Eugenii P
authors.initials: EP
authors.lastname: Khizhnyak
authors.affiliation: Zakusov Research Institute of Pharmacology of RAMS, Moscow, Russia.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Anisina
authors.affiliation: Zakusov Research Institute of Pharmacology of RAMS, Moscow, Russia.
authors.forename: Andrei D
authors.initials: AD
authors.lastname: Durnev
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D020552:Comet Assay / Q000592:standards*; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D007753:Laboratories / Q000592:standards*; D008741:Methyl Methanesulfonate / Q000633:toxicity; D051379:Mice; D008810:Mice, Inbred C57BL; D014965:X-Rays / Q000009:adverse effects
chemical_list: D008741:Methyl Methanesulfonate
keywords: Alkaline electrophoresis; Bone marrow cells; Comet assay; DNA damage; MMS; X-ray