Non-invasive Monitoring of L-2-Oxothiazolidine-4-Carboxylate Metabolism in the Rat Brain by In vivo 13C Magnetic Resonance Spectroscopy

Abstract

The cysteine precursor L-2-oxothiazolidine-4-carboxylate (OTZ, procysteine) can raise cysteine concentration, and thus glutathione levels, in some tissues. OTZ has therefore been proposed as a prodrug for combating oxidative stress. We have synthesized stable isotope labeled OTZ (i.e. L-2-oxo-[5-13 C]-thiazolidine-4-carboxylate, 13 C-OTZ) and tracked its uptake and metabolism in vivo in rat brain by 13 C magnetic resonance spectroscopy. Although uptake and clearance of 13 C-OTZ was detectable in rat brain following a bolus dose by in vivo spectroscopy, no incorporation of isotope label into brain glutathione was detectable. Continuous infusion of 13 C-OTZ over 20 h, however, resulted in 13 C-label incorporation into glutathione, taurine, hypotaurine and lactate at levels sufficient for detection by in vivo magnetic resonance spectroscopy. Examination of brain tissue extracts by mass spectrometry confirmed only low levels of isotope incorporation into glutathione in rats treated with a bolus dose and much higher levels after 20 h of continuous infusion. In contrast to some previous studies, bolus administration of OTZ did not alter brain glutathione levels. Even a continuous infusion of OTZ over 20 h failed to raise brain glutathione levels. These studies demonstrate the utility of in vivo magnetic resonance for non-invasive monitoring of antioxidant uptake and metabolism in intact brain. These types of experiments can be used to evaluate the efficacy of various interventions for maintenance of brain glutathione.

Synthesis of 13C‐labeled derivatives of cysteine for magnetic resonance imaging studies of drug uptake and conversion to glutathione in rat brain

“…Three prodrugs derived from cysteine were synthesized with 13 C‐labeling such that the in vivo uptake of each and conversion to glutathione in the brain could be monitored by magnetic resonance imaging; such a study using the [ 13 C]‐OTZ has been completed in rats . Continuous infusion of [ 13 C]‐OTZ over 20 hours allowed for the detection of 13 C‐glutathione as well as several labeled metabolites derived from OTZ.…”