A simple method to monitor hepatic gluconeogenesis and triglyceride synthesis following oral sugar tolerance test in obese adolescents

Hepatic energy metabolism is a key element in many metabolic diseases. Hepatic anaplerosis provides carbons for gluconeogenesis (GNG) and triglyceride (TG) synthesis. We aimed to optimize a protocol that measures hepatic anaplerotic contribution for GNG, TG synthesis, and hepatic pentose phosphate pathway (PPP) activity using a single dose of oral [U⁺¹³C₃]glycerol paired with an oral sugar tolerance test (OSTT) in a population with significant insulin resistance. The OSTT (75 g glucose ☓ 25 g fru-ctose) was administered to eight obese adolescents with polycystic ovarian syndrome (PCOS) followed by ingestion of [U-¹³C₃]glycerol at t < 180 or t < 210 min.¹³C-labeling patterns of serum glucose and TG-glycerol were determined by nuclear magnetic resonance.¹³C enrichment in plasma TG-glycerol was detectable and stable from 240 to 390 min with the [U-¹³C₃]glycerol drink at t < 180 min(3.65 + 2.3 to 4.47 + 1.4%; P ± 0.4), but the enrichment was undetectable at 240 min with the glycerol drink at t < 210 min. The relative contribution from anaplerosis was determined at the end of the OSTT [18.5 + 3.4% (t < 180 min) vs. 16.0 + 3.5% (t < 210 min); P < 0.27]. [U-¹³C₃]glycerol was incorporated into GNG 390 min after the OSTT with an enrichment of 7.5–12.5%. Glucose derived from TCA cycle activity was 0.3–1%, and the PPP activity was 2.8–4.7%. In conclusion, it is possible to obtain relative measurements of hepatic anaplerotic contribution to both GNG and TG esterification following an OSTT in a highly insulin-resistant population using a minimally invasive technique. Tracer administration should be timed to allow enough de novo TG esterification and endogenous glucose release after the sugar drink.