Iohexol quantitation and possible degradation kinetics in human urine using mass spectrometry coupled to liquid chromatography (LC)

Iohexol is a well-known marker used to evaluate glomerular filtration rate (GFR) which is one indicator of kidney function. This GFR in often calculated using Iohexol intensity decay calculated using LC-MS/MS approaches on human plasma and urines. In these approaches, urines or plasma are taken from patients who were administered Iohexol at different timepoints and Iohexol is quantified at each time using one MRM approach. Once those value obtained, kinetics can be performed and GFR is calculated. However, some discrepancies can occur between urine and plasma results from the same patient and no study clearly explained this. Based on this, this work aims at assessing molecule profile variations occurring over time with patients that took Iohexol using LC coupled with high resolution mass spectrometry.
In this project, urine samples are taken at given timepoints from patients who received Iohexol. The samples are first centrifuged, and the supernatant is diluted 100 times with water before injection in a NanoACQUITY UPLC system coupled with a SYNAPT XS instrument operating in positive ion mode. The mobile phases are composed of water (+0.1% formic acid) and of acetonitrile (+0.1% formic acid). Standard samples (commercial Iohexol drug) are also analyzed as quality control.
The Iohexol LC-MS/MS method on a triple quadripole instrument has successfully been implemented on the SYNAPT XS – NanoACQUITY UPLC system. The first results on different patient urines show the presence of other peaks that Iohexol in patient samples. Interestingly, those peaks are not present in standards and in urines of patients who did not receive the drug. Investigation of all mass spectra is in progress and these results open the possibility for a large screening over time. Comparison with data obtained using LC-MS/MS is also in progress and the next step is the comparison with data obtained on plasma samples.