Simultaneous LC-MS/MS analysis of the biomarkers cAMP and cGMP in plasma, CSF and brain tissue.

The cyclic nucleotides cyclic adenosine-3',5'-monophosphate (cAMP) and cyclic guanosine-3',5'-monophosphate (cGMP) are important second messengers. They are useful biomarkers to indicate biological activity of drugs such as phosphodiesterase (PDE) inhibitors which block the degradation of these nucleotides. Here, we established a fast and sensitive method for the simultaneous analysis of cAMP and cGMP by LC-MS/MS with broad applicability. The limit of detection is 50 pM. Linearity is given in a range of 0.5-500 nM for both nucleotides, with a high intra- and inter-assay precision and accuracy and an analysis time of 3.5 min. We validated the suitability of the method by pharmacological modulation of cAMP or cGMP concentrations in mice with the PDE4 inhibitor rolipram and the PDE5 inhibitor zaprinast. Rolipram significantly increased cAMP concentrations in plasma, CSF and brain tissue. Zaprinast increased cGMP concentrations in plasma but not in brain tissue, which is in accordance with its blood brain barrier permeability. In conclusion, the LC-MS/MS method described here could be a valuable analytical tool for investigating pharmacodynamic effects of PDE inhibitors and to monitor disease-related changes of cAMP and cGMP in the periphery as well as in the central nervous system.