The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay is one of the most commonly used tests of cell proliferation. Hydralazine has been reported to interfere with the performance of the MTS assay when used on adherent cells. This study aimed to investigate whether hydralazine interferes with the performance of the MTS assay on suspended cells. THP-1 (a monocytic leukemia cell line) cells were cultured in the presence or absence of hydralazine (0, 10, 50, 100, and 500 μM) for 2 or 24 h. Cell numbers were analyzed using the MTS, trypan blue exclusion, or microscopic assays. A modified version of the standard MTS assay was established by centrifuging the cells and replacing the test medium with fresh culture medium immediately before the addition of the MTS reagent. Culture of THP-1 cells with hydralazine at concentrations of 50, 100, and 500 μM for 2 h increased absorbance (p < 0.001) in the standard MTS assay, whereas both the trypan blue exclusion assay and microscopy suggested no change in cell numbers. Culture of THP-1 cells with 100 and 500 μm hydralazine for 24 h increased absorbance (p < 0.05) in the standard MTS assay; however, trypan blue exclusion and microscopy suggested a decrease in cell numbers. In a cell-free system, hydralazine (100 and 500 μM) increased absorbance in a time- and concentration-dependent manner. The modified MTS assay produced results consistent with trypan blue exclusion and microscopy using THP-1 cells. In addition, the modified MTS assay produced reliable results when K562 and Jurkat cells were incubated with hydralazine or β-mercaptoethanol (βME). In conclusion, a simple modification of the standard MTS assay overcame the interference of hydralazine and βME when assessing suspended cells.

中文翻译：

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一种改进的 MTS 悬浮细胞增殖试验，以避免肼和 β-巯基乙醇的干扰

3-(4,5-二甲基噻唑-2-基)-5-(3-羧基甲氧基苯基)-2-(4-磺基苯基)-2H-四唑鎓 (MTS) 测定是最常用的细胞增殖测试之一。据报道，肼苯哒嗪用于贴壁细胞时会干扰 MTS 检测的性能。本研究旨在调查肼苯哒嗪是否会干扰 MTS 测定对悬浮细胞的性能。在存在或不存在肼苯哒嗪（0、10、50、100 和 500 μM）的情况下，将 THP-1（一种单核细胞白血病细胞系）细胞培养 2 或 24 小时。使用 MTS、台盼蓝排除法或显微测定法分析细胞数。通过在加入 MTS 试剂之前立即将细胞离心并用新鲜培养基替换测试培养基来建立标准 MTS 测定的改进版本。在标准 MTS 测定中，将 THP-1 细胞与肼苯哒嗪以 50、100 和 500 μM 的浓度培养 2 小时会增加吸光度（p < 0.001），而台盼蓝排除测定和显微镜检查均表明细胞数量没有变化。在标准 MTS 测定中，用 100 和 500 μm 肼苯哒嗪培养 THP-1 细胞 24 小时会增加吸光度（p < 0.05）；然而，台盼蓝排除和显微镜检查表明细胞数量减少。在无细胞系统中，肼苯哒嗪（100 和 500 μM）以时间和浓度依赖性方式增加吸光度。改进的 MTS 测定产生的结果与台盼蓝排除和使用 THP-1 细胞的显微镜检查一致。此外，当 K562 和 Jurkat 细胞与肼苯哒嗪或 β-巯基乙醇 (βME) 一起孵育时，改进的 MTS 测定产生了可靠的结果。综上所述，