TY - JOUR
T1 - Transaldolase exchange and its effects on measurements of gluconeogenesis in humans
AU - Basu, Rita
AU - Barosa, Cristina
AU - Basu, Ananda
AU - Pattan, Vishwanath
AU - Saad, Ahmed
AU - Jones, John
AU - Rizza, Robert
PY - 2011/2
Y1 - 2011/2
N2 - The deuterated water method is used extensively to measure gluconeogenesis in humans. This method assumes negligible exchange of the lower three carbons of fructose 6-phsophate via transaldolase exchange since this exchange will result in enrichment of carbon 5 of glucose in the absence of net gluconeogenesis. The present studies tested this assumption. 2H2O and acetaminophen were ingested and [1-13C]acetate infused in 11 nondiabetic subjects after a 16-h fast. Plasma and urinary glucuronide enrichments were measured using nuclear magnetic resonance spectroscopy before and during a 0.35 mU•kg FFM-1•min-1 insulin infusion. Rates of endogenous glucose production measured with [3- 3H]- and [6,6-2H2]glucose did not differ either before (14.0 ± 0.7 vs. 13.8 ± 0.7 μmol•kg -1•min-1) or during the clamp (10.4 ± 0.9 vs. 10.9 ± 0.7 μmol•kg-1•min-1), consistent with equilibration and quantitative removal of tritium during triose isomerase exchange. Plasma [3-13C] glucose-to-[4-13C] glucose and urinary [3-13C] glucuronide-to-[4-13C] glucuronide ratios were <1.0 (P < 0.001) in all subjects both before (0.66 ± 0.04 and 0.60 ± 0.04) and during (059 ± 0.05 and 0.56 ± 0.06) the insulin infusion, respectively, indicating that ∼35-45% of the labeling of the 5th carbon of glucose by deuterium was due to transaldolase exchange rather than gluconeogenesis. When corrected for transaldolase exchange, rates of gluconeogenesis were lower (P < 0.001) and glycogenolysis higher (P < 0.001) than uncorrected rates both before and during the insulin infusion. In conclusion, assuming negligible dilution by glycerol and near-complete triose isomerase equilibration, these data provide strong experimental evidence that transaldolase exchange occurs in humans, resulting in an overestimate of gluconeogenesis and an underestimate of glycogenolysis when measured with the 2H2O method. Use of appropriate 13C tracers provides a means of correcting for transaldolase exchange.
AB - The deuterated water method is used extensively to measure gluconeogenesis in humans. This method assumes negligible exchange of the lower three carbons of fructose 6-phsophate via transaldolase exchange since this exchange will result in enrichment of carbon 5 of glucose in the absence of net gluconeogenesis. The present studies tested this assumption. 2H2O and acetaminophen were ingested and [1-13C]acetate infused in 11 nondiabetic subjects after a 16-h fast. Plasma and urinary glucuronide enrichments were measured using nuclear magnetic resonance spectroscopy before and during a 0.35 mU•kg FFM-1•min-1 insulin infusion. Rates of endogenous glucose production measured with [3- 3H]- and [6,6-2H2]glucose did not differ either before (14.0 ± 0.7 vs. 13.8 ± 0.7 μmol•kg -1•min-1) or during the clamp (10.4 ± 0.9 vs. 10.9 ± 0.7 μmol•kg-1•min-1), consistent with equilibration and quantitative removal of tritium during triose isomerase exchange. Plasma [3-13C] glucose-to-[4-13C] glucose and urinary [3-13C] glucuronide-to-[4-13C] glucuronide ratios were <1.0 (P < 0.001) in all subjects both before (0.66 ± 0.04 and 0.60 ± 0.04) and during (059 ± 0.05 and 0.56 ± 0.06) the insulin infusion, respectively, indicating that ∼35-45% of the labeling of the 5th carbon of glucose by deuterium was due to transaldolase exchange rather than gluconeogenesis. When corrected for transaldolase exchange, rates of gluconeogenesis were lower (P < 0.001) and glycogenolysis higher (P < 0.001) than uncorrected rates both before and during the insulin infusion. In conclusion, assuming negligible dilution by glycerol and near-complete triose isomerase equilibration, these data provide strong experimental evidence that transaldolase exchange occurs in humans, resulting in an overestimate of gluconeogenesis and an underestimate of glycogenolysis when measured with the 2H2O method. Use of appropriate 13C tracers provides a means of correcting for transaldolase exchange.
KW - Deuterated water method
KW - Endogenous glucose production
KW - Transaldolase exchange reaction
KW - Triosephosphate isomerase
KW - [3-H]glucose
KW - [6,6- H]glucose
UR - http://www.scopus.com/inward/record.url?scp=79251576452&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79251576452&partnerID=8YFLogxK
U2 - 10.1152/ajpendo.00403.2010
DO - 10.1152/ajpendo.00403.2010
M3 - Article
C2 - 21062960
AN - SCOPUS:79251576452
SN - 0193-1849
VL - 300
SP - E296-E303
JO - American Journal of Physiology - Endocrinology and Metabolism
JF - American Journal of Physiology - Endocrinology and Metabolism
IS - 2
ER -