The formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay is widely used for the measurement of oxidatively generated damage to DNA. However, there has not been a recommended long-term positive control for this version of the comet assay. We have investigated potassium bromate as a positive control for the Fpg-modified comet assay because it generates many Fpg-sensitive sites with little concurrent generation of DNA strand breaks. Eight laboratories used the same procedure for the treatment of monocytic THP-1 cells with potassium bromate (0, 0.5, 1.5 and 4.5 mM) and subsequent cryopreservation in freezing medium consisting of 50% foetal bovine serum, 40% RPMI-1640 medium and 10% dimethyl sulphoxide. The samples were analysed by the Fpg-modified comet assay three times over a three-year period. All laboratories obtained positive concentration-response relationship in cryopreserved samples (linear regression coefficients ranging from 0.79 to 0.99). However, there was a wide difference in the levels of Fpg-sensitive sites between laboratory with the lowest (4.2% Tail DNA) and highest (74% Tail DNA) values in THP-1 cells after exposure to 4.5 mM KBrO3. In an attempt to assess sources of inter-laboratory variation in Fpg-sensitive sites, comet images from one experiment in each laboratory were forwarded to a central laboratory for visual scoring. There was high consistency between measurements of %Tail DNA values in each laboratory and the visual score of the same comets done in the central laboratory (r = 0.98, P < 0.001, linear regression). In conclusion, the results show that potassium bromate is a suitable positive comet assay control.

中文翻译：

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长期冷冻保存溴酸钾阳性测定对照，用于通过 Fpg 改良彗星测定测量氧化损伤的 DNA：hCOMET 环试验的结果

甲酰胺嘧啶 DNA 糖基化酶 (Fpg) 改良彗星测定广泛用于测量 DNA 氧化损伤。然而，对于这个版本的彗星测定，还没有推荐的长期阳性对照。我们研究了溴酸钾作为 Fpg 改良彗星测定的阳性对照，因为它会产生许多 Fpg 敏感位点，几乎不会同时产生 DNA 链断裂。八个实验室使用相同的程序用溴酸钾（0、0.5、1.5 和 4.5 mM）处理单核 THP-1 细胞，然后在由 50% 胎牛血清、40% RPMI-1640 培养基和 10% 组成的冷冻培养基中冷冻保存。 ％二甲亚砜。在三年内，通过 Fpg 改良彗星试验对样本进行了 3 次分析。所有实验室在冷冻保存的样品中都获得了正浓度-反应关系（线性回归系数范围为 0.79 至 0.99）。然而，暴露于 4.5 mM KBrO3 后，THP-1 细胞中 Fpg 敏感位点水平在实验室之间存在很大差异，最低值（4.2% 尾部 DNA）和最高值（74% 尾部 DNA）。为了评估 Fpg 敏感位点的实验室间变异来源，每个实验室的一项实验的彗星图像被转发到中央实验室进行视觉评分。每个实验室的％尾部DNA值测量值与中心实验室对相同彗星进行的视觉评分之间存在高度一致性（r = 0.98，P < 0.001，线性回归）。总之，结果表明溴酸钾是合适的彗星试验阳性对照。