Assessing the pentose phosphate pathway using [2, 3-¹³C₂]glucose

The pentose phosphate pathway (PPP) is essential for reductive biosynthesis, antioxidant processes and nucleotide production. Common tracers such as [1,2-¹³C₂]glucose rely on detection of ¹³C in lactate and require assumptions to correct natural ¹³C abundance. Here, we introduce a novel and specific tracer of the PPP, [2,3-¹³C₂]glucose. ¹³C NMR analysis of the resulting isotopomers is informative because [1,2-¹³C₂]lactate arises from glycolysis and [2,3-¹³C₂]lactate arises exclusively through the PPP. A correction for natural abundance is unnecessary. In rats receiving [2,3-¹³C₂]glucose, the PPP was more active in the fed versus fasted state in the liver and the heart, consistent with increased expression of key enzymes in the PPP. Both the PPP and glycolysis were substantially increased in hepatoma compared with liver. In summary, [2,3-¹³C₂]glucose and ¹³C NMR simplify assessment of the PPP.