Mass Spectrometry for the Sensitive Analysis of Intracellular Nucleotides and Analogues

Abstract

Nowadays, mass spectrometry is very important and widely applied tool in nucleotide analysis. As a result of technological advances in sample preparation, separation and mass spectrometry detection, the developed methods allow sensitive and selective measurement of polar compounds occurring in low levels in various biological matrices. This enables more potential uses in clinical field. Direct methods require no special sample pre-treatment before analysis in contrast to indirect methods, where fractionation, dephosphorylation and purification are needed. The use of ion-pairing agent, ion exchange chromatography with pH gradient, porous graphitic carbon columns and HILIC in liquid chromatography represents the most common methods of nucleotide analysis. High separation efficiency is also achieved with the use of CE with MS detection. Analysis of nucleotides was also described by the means of MALDI-TOF, but poor reproducibility and lack of applications make a limitation for this approach. The chapter summarizes different techniques and approaches for determination of endogenous nucleotides and its analogues in various clinical applications. or deoxyribose) through a glycosidic bond. Nucleotides are formed by phosphorylation of nucleoside molecule. They represent a fundamental building block of the structure of nucleic acids formed by the polymerase-mediated synthesis of DNA and RNA from deoxynucleotides and nucleotides, respectively. All deoxynucleotides are synthesized from the corresponding nucleotides. Nucleotides play another important role in enzyme activation and metabolism. They are incorporated into important cofactors of enzymatic reactions such as transfer of various groups by coenzyme A (e.g. acetyl-CoA and succinyl-CoA) in many metabolic processes, NAD, NADP and FAD as coenzymes of oxidoreductases catalyses redox reactions in the cell. ATP and other nucleoside triphosphates are engaged as source energy providers. In the form of coenzymes, they transfer phosphate residues or nucleotide constituent and participate in the activation (e.g. uridine diphosphate glucose for pasting glucose units to polymeric saccharides or cytidine diphosphate-choline for phospholipid synthesis). Cyclic nucleotides act as secondary messengers in many signal transduction pathways. The most important nucleotide signal molecule is cyclic adenosine monophosphate (cAMP), which is an activator of protein kinases and participates in many metabolic pathways by transferring the effect of hormones into cells. Analogical molecule-cyclic guanosine monophosphate (cGMP)-also acts as a secondary messenger in the phototransduction process.Nucleotide metabolism is one of the main therapeutic cellular targets. Synthetic analogues of these compounds have been widely applied in anti-cancer, anti-viral and immunosuppressive therapies [1][2][3][4][5][6]. Nucleoside analogues (e.g. cytarabine, gemcitabine and zidovudine) are modified at the base or sugar moiety. This 'prodrug' form requires intracellular activation by phosphorylation to mono, di or...