Changes in mutagenicity and acute toxicity of solutions of iodinated X-ray contrast media during chlorination

In the present study, the effects of chlorination on the mutagenicity (assessed via the Ames assay) and acute toxicity (assessed via a bioluminescence inhibition assay) of solutions containing one of five commonly used iodinated X-ray contrast media (ICM) (iopamidol, iohexol, iopromide, iomeprol, and diatrizoate) were investigated. Of the five ICM tested, only iopamidol was degraded by chlorine. Chlorination of the iopamidol-containing solution induced both mutagenicity and acute toxicity, which increased with chlorination time (up to 96 h). The areas of five out of 54 peaks detected on the LC/MS total ion chromatogram had good correlation (r2 > 0.90) between peak area and observed mutagenicity. To identify possible contributors to the observed mutagenicity, the Ames assay and LC/MS analysis were conducted on samples collected at 48-h chlorination time and extracted under different pH conditions. Of the five peaks, one peak was detected in the sample extracted at pH 7, but this sample was not mutagenic, indicating that the peak was not related to the observed mutagenicity. MS/MS analysis with an orbitrap mass spectrometer of the remaining four peaks revealed that two of the peaks represented the same TP (detected in negative and positive ion modes). Finally, three TPs were identified as suspected contributors to the mutagenicity induced by the iopamidol-containing solution after chlorination: 5-[(1,3-dihydroxypropan-2-yl)carbamoyl]-3-[(3-hydroxypropanoyl)oxy]-2,4-diiodobenzoic acid; N-(1,3-dihydroxypropan-2-yl)-3-(2,3-dioxopropyl)-2,4,6-triiodobenzamide; and 3-[(1,3-dihydroxypropan-2-yl)carbamoyl]-5-[(3-hydroxybutanoyl)oxy]-2,4,6-triiodobenzoic acid. Prediction of the mutagenicity potential of these three TPs with a battery of four quantitative structure-activity relationship models did not contradict our conclusion that these TPs contributed to the observed mutagenicity.