Real-Time Nuclear Magnetic Resonance Detection of Fumarase Activity Using Parahydrogen-Hyperpolarized [1-¹³C]Fumarate

Hyperpolarized fumarate can be used as a probe of real-time metabolism in vivo, using carbon-13 magnetic resonance imaging. Dissolution dynamic nuclear polarization is commonly used to produce hyperpolarized fumarate, but a cheaper and faster alternative is to produce hyperpolarized fumarate via PHIP (parahydrogen-induced polarization). In this work, we trans-hydrogenate [1-¹³C]acetylene dicarboxylate with para-enriched hydrogen using a commercially available Ru catalyst in water to produce hyperpolarized [1-¹³C]fumarate. We show that fumarate is produced in 89% yield, with succinate as a side product in 11% yield. The proton polarization is converted into ¹³C magnetization using a constant adiabaticity field cycle, and a polarization level of 24% is achieved using 86% para-enriched hydrogen gas. We inject the hyperpolarized [1-¹³C]fumarate into cell suspensions and track the metabolism. This work opens the path to greatly accelerated preclinical studies using fumarate as a biomarker.