Validation of a sensitive LC/MSMS method for chloronucleoside analysis in biological matrixes and its applications

Myeloperoxidase promotes several kinds of damage and is involved in the development of various diseases (as atherosclerosis and cancers). An example of these damage is the chlorination of nucleic acids, which is considered as a specific marker of the MPO activity on those acids. This study aimed to develop and validate a method to analyze oxidized and MPO-specific chlorinated nucleosides in biological matrixes (cells, tissues and plasma). Although a lot of methods to quantify oxidized or chlorinated nucleosides have already been established, none of them took into account all these derivatives together. The new method used a Triple Quadrupole mass spectrometer fitted with a Jet Stream electrospray ionization source. This approach has two advantages compared with existing LC/MSMS analyses: it includes MPO-induced modifications in a unique analysis and obtains a better sensitivity. Our optimized method reached LOQs of 1.50pg and 1.42pg respectively for oxoG and oxo(d)G, being 4 times more sensitive than previous methods, and LOQs of 1.39pg, 1.30pg and 63.4 fg respectively for 5-chlorocytidine, 5-chloro-2'-deoxycytidine and 8-chloroguanosine. Developed method is also 25 times more sensitive for chloroguanosine than the best existing method. Nevertheless, this method is not specific enough for 8-chloro-(2'-deoxy)adenosine analysis. Examples of applications demonstrate the interest of this validated method. Indeed analysis of plasma from healthy donors highlighted exclusively the presence of 5-chlorocytidine (1.0±0.2nM) whereas analysis of treated endothelial cells by HOCl showed chlorination of guanosine and cytidine in cytoplasmic pools and chlorination of (deoxy)cytidine in DNA and RNA. In conclusion, this study shows that 5-chloro-2'-deoxycytidine, 5-chlorocytidine and 8-chloroguanosine are good markers allowing us to detect the MPO activity in biological fluids. The robust, specific and sensitive developed method enables future studies on MPO implications in human diseases.