Determination of cyclic guanosine- and cyclic adenosine monophosphate (cGMP and cAMP) in human plasma and animal tissues by solid phase extraction on silica and liquid chromatography–triple quadrupole mass spectrometry

3′,5′-Cyclic guanosine monophosphate (cGMP) and 3′,5′-cyclic adenosine monophosphate (cAMP) are essential second messenger molecules. They are involved in signal transduction within cells, in physiological functions such as neurotransmission and in the modulation of cell growth and differentiation of organisms, respectively. A quantitative solid phase extraction method (SPE) based on hydrophilic interaction on silica was developed and applied to both plasma and tissue samples. The stable isotope-labeled internal standards 2D1,15N3-3′,5′-cGMP and 13C10,15N5-3′,5′-cAMP were added prior to the sample preparation to ensure high precision and accuracy. The samples were analyzed by reversed-phase liquid chromatography (RP-LC). Negative electrospray (ESI)-MS/MS was used to selectively monitor several transitions of each metabolite. The method for the analysis of 3′,5′-cAMP and 3′,5′-cGMP in plasma was validated in the range of 0.15–20 ng/mL (R2 = 0.9996 and 0.9994 for 3′,5′-cAMP and 3′,5′-cGMP, respectively). Basal plasma concentrations for fifteen healthy human patients determined with this method varied between 4.66–9.20 ng/mL for 3′,5′-cAMP and between 0.30–1.20 ng/mL for 3′,5′-cGMP, with precisions better than 9.1%. 3′,5′-cGMP and 3′,5′-cAMP together with their 2′,3′-isomers were also determined in a semi quantitative way in animal tissues. The structures of the isomers were confirmed by analysis with LC-high resolution time-of-flight MS and subsequently by comparison of retention times with standards.