Molecular correlates of MRS-based 31 phosphocreatine muscle resynthesis rate in healthy adults.

Dynamic phosphorus MRS (31 P-MRS) is a method used for in vivo studies of skeletal muscle energetics including measurements of phosphocreatine (PCr) resynthesis rate during recovery of submaximal exercise. However, the molecular events associated with the PCr resynthesis rate are still under debate. We assessed vastus lateralis PCr resynthesis rate from 31 P-MRS spectra collected from healthy adults as part of the CALERIE II study (caloric restriction), and assessed associations between PCr resynthesis and muscle mitochondrial signature transcripts and proteins (NAMPT, NQO1, PGC-1α, and SIRT1). Regression analysis indicated that higher concentration of nicotinamide phosphoribosyltransferase (NAMPT) protein, a mitochondrial capacity marker, was associated with faster PCr resynthesis. However, PCr resynthesis was not associated with greater physical fitness (VO2 peak) or messenger ribonucleic acid levels of mitochondrial function markers such as NQO1, PGC-1α, and SIRT1, suggesting that the impact of these molecular signatures on PCr resynthesis may be minimal in the context of an acute exercise bout. Together, these findings suggest that 31 P-MRS based PCr resynthesis may represent a valid non-invasive surrogate marker of mitochondrial NAMPT in human skeletal muscle.

Automated concentration of [18F]fluoride into microliter volumes.

Concentration of [18F]fluoride has been mentioned in literature, however, reports have lacked details about system designs, operation, and performance. Here, we describe in detail a compact, fast, fully-automated concentration system based on a micro-sized strong anion exchange cartridge. The concentration of radionuclides enables scaled-up microfluidic synthesis. Our system can also be used to provide highly concentrated [18F]fluoride with minimal water content. We demonstrate how the concentrator can produce varying concentrations of [18F]fluoride for the macroscale synthesis of N-boc-5-[18F]fluoroindole without an azeotropic drying process, while enabling high starting radioactivity. By appropriate choice of solid-phase resin, flow conditions, and eluent solution, we believe this approach can be extended beyond [18F]fluoride to other radionuclides.

Performing multi-step chemical reactions in microliter-sized droplets by leveraging a simple passive transport mechanism.

Despite the increasing importance of positron emission tomography (PET) imaging in research and clinical management of disease, access to myriad new radioactive tracers is severely limited due to their short half-lives (which requires daily production) and the high cost and complexity of tracer production. The application of droplet microfluidics based on electrowetting-on-dielectric (EWOD) to the field of radiochemistry can significantly reduce the amount of radiation shielding necessary for safety and the amount of precursor and other reagents needed for the synthesis. Furthermore, significant improvements in the molar activity of the tracers have been observed. However, widespread use of this technology is currently hindered in part by the high cost of prototype chips and the operating complexity. To address these issues, we developed a novel microfluidic device based on patterned wettability for multi-step radiochemical reactions in microliter droplets and implemented automated systems for reagent loading and collection of the crude product after synthesis. In this paper, we describe a simple and inexpensive method for fabricating the chips, demonstrate the feasibility of prototype chips for performing multi-step radiochemical reactions to produce the PET tracers [18F]fallypride and [18F]FDG, and further show that synthesized [18F]fallypride can be used for in vivo mouse imaging.