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Mass spectrometric studies on the in vitro generated metabolites of SIRT1 activating drugs for doping control purposes.

The enzyme SIRT1 is a metabolic key regulator in mitochondrial biogenesis, fat and glucose metabolism. Its activation through pharmaceutical SIRT1 activators such as SRT2104 results in an increased deacetylation of substrates representing important targets for the treatment of metabolic diseases. Moreover, SRT1720 was found to enhance the physical performance of mice. As SIRT1 activators might therefore be relevant in a doping control context, metabolism studies of target substances need be conducted in order to develop a detection assay for SIRT1 activators in urine. In the present study, the in vitro metabolism of five SIRT1 activators was investigated using human liver microsomes. The mass spectrometric behavior of the resulting metabolites following positive electrospray ionization and collision-induced dissociation was elucidated by high-resolution/high-accuracy (tandem) mass spectrometry, and confirmation of the structure of a major metabolite of SRT1720 was accomplished by chemical synthesis. Subsequently, a screening procedure for urine samples was developed employing liquid-liquid-extraction and liquid chromatography/tandem mass spectrometry based on diagnostic ion transitions recorded in multiple reaction monitoring mode and the use of d8-SRT1720 as deuterated internal standard. The method was validated with regard to specificity, sensitivity (limit of detection 0.5 ng/ml), recovery (88-99%) and imprecision (7-18%) as well as ion suppression/enhancement effects (<10%), demonstrating its fitness-for-purpose for sports drug testing applications.