Emily Buchanan

Abstract: Hyperpolarized 15N NAD+/ NADH Mimetics as Redox-Responsive MRI Sensors
Redox responsive sensors for imaging the redox state of tissues are highly desirable for detection and assessment of a number of clinical conditions including hypoxic tumors, oxidative stress, and various stages of common liver diseases. The goal of this project was to develop 15N NMR probes that mimic the redox action of the cofactors, NAD+/NADH. We used hyperpolarized NMR technology (microwave driven dynamic nuclear polarization) to amplify the 15N NMR signal in order to facilitate the observation of this low sensitivity nucleus. As the hyperpolarized magnetization decays by T1 (spin-lattice) relaxation, the use of 15N in hyperpolarized NMR/MRI is a promising because of the long T1 of many 15N compounds. The oxidized form of our NAD+/NADH mimetic, [1-15N]-3-carbamoyl-1-methylpyridin-1-ium-iodide, was synthesized from 15N labeled nicotinamide as shown in the figure. The compound was reduced with sodium dithionite to afford the reduced form, [1-15N]-3-carbamoyl-1,4-dihydro-1-methylpyridine. Conventional 15N NMR spectroscopy at 9.4 T revealed that there was a dramatic chemical shift difference (124.2 ppm) between the oxidized and reduced forms. The oxidized form was hyperpolarized by dynamic nuclear polarization (DNP) in a commercially available clinical polarizer (SPINlab) using trityl OX063 free radical as polarizing agent followed by dissolution with superheated water. The hyperpolarized 15N signal was recorded at 1T after dissolution. The decay of the hyperpolarized 15N magnetization afforded a spin-lattice (T1) relaxation time of 180 s at 1T. The long T1’s and the large chemical shift differences between the oxidized and reduced forms demonstrate the exciting potential for their use as 15N NMR/MRI redox sensors.
 

What does research mean to you?
To me, research means the freedom to ask new questions and then hunt down answers. Research requires creativity, and a constant desire to push the boundaries of current knowledge. As a research student, I love being able to find creative ways to solve complex problems.
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Tell us about your journey.
During my last year of high school, I had the opportunity to work in a Mass Spectrometry lab at the University of North Texas where I fell in love with research. In particular, I enjoyed thinking about how we use and develop instruments to monitor biological processes. After this experience, I decided to pursue a degree in Chemistry at UT Dallas where I could continue working on research projects and hopefully someday be a Green Fellow!

During my undergraduate, I researched with several labs as a summer REU/SURF student. At UT Austin I got to dive further into Mass Spectrometry research and its applications in forensics and medicine as part of the Eberlin group. The next summer, since I could not be physically in lab due to the pandemic, I continued researching as part of virtual NASA Undergraduate team working on lunar water extraction technologies. During the school year, I worked on smaller research projects for a local cardiology and ophthalmology clinic so that I could focus on my coursework.

I applied and was accepted as a Green Fellow during my Junior year. Excited to explore a different side of Chemistry, I joined the Kovacs group which develops NMR/MRI probes and hyperpolarized NMR/MRI agents to noninvasively detect disease and study metabolism. After my Green Fellowship, I joined with the Magnetic Imaging Group at NIST as a summer SURF student working on pulse sequence programing for a microMRI system.

What was your favorite part about the program?
I really enjoyed the freedom that came with being a Green Fellow. I expected to be under the guidance of a graduate student, but I had the opportunity to work directly with my PI. I was able to dive into headfirst into my project. I planned my own experiments, troubleshooted with my Dr. Kovacs when things went wrong, and presented my findings to the rest of the group when my experiments were a success. Overall, this immersive experience made me much more confident in the lab.

What was the biggest thing you learned from the program?
In many of my prior research experiences I had worked with a smaller group or under one graduate student. In my UTSW lab, I have really enjoyed getting to work with a much larger team. I have learned about NMR/MRI technology from many different perspectives and have enjoyed learning how each researcher helps optimize imaging experiments. I have also enjoyed learning about some of the practical planning that goes into human studies and how collaboration makes these efforts possible.

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Advice for Future Green Fellows

Ask as many questions as possible and try to learn everything you can about your experimental protocol. Be curious and engaged! On a more practical note, start preparing your presentation ahead of time. While working through background literature or analyzing data, take the time to prepare initial slides and figures so you don’t have to rush at the end of the program.