²H enrichment distribution of hepatic glycogen from²H₂O reveals the contribution of dietary fructose to glycogen synthesis

Abstract

Delgado TC, Martins FO, Carvalho F, Gonçalves A, Scott DK, O'Doherty R, Macedo MP, Jones JG.2 H enrichment distribution of hepatic glycogen from 2 H2O reveals the contribution of dietary fructose to glycogen synthesis. Am J Physiol Endocrinol Metab 304: E384 -E391, 2013. First published December 4, 2012; doi:10.1152/ajpendo.00185.2012.-Dietary fructose can benefit or hinder glycemic control, depending on the quantity consumed, and these contrasting effects are reflected by alterations in postprandial hepatic glycogen synthesis. Recently, we showed that 2 H enrichment of glycogen positions 5 and 2 from deuterated water ( 2 H2O) informs direct and indirect pathway contributions to glycogenesis in naturally feeding rats. Inclusion of position 6S 2 H enrichment data allows indirect pathway sources to be further resolved into triose phosphate and Krebs cycle precursors. This analysis was applied to six rats that had fed on standard chow (SC) and six rats that had fed on SC plus 35% sucrose in their drinking water (HS). After 2 wk, hepatic glycogenesis sources during overnight feeding were determined by 2 H2O administration and postmortem analysis of glycogen 2 H enrichment at the conclusion of the dark period. Net overnight hepatic glycogenesis was similar between SC and HS rodents. Whereas direct pathway contributions were similar (403 Ϯ 71 mol/g dry wt HS vs. 578 Ϯ 76 mol/g dry wt SC), triose phosphate contributions were significantly higher for HS compared with SC (382 Ϯ 61 vs. 87 Ϯ 24 mol/g dry wt, P Ͻ 0.01) and Krebs cycle inputs lower for HS compared with SC (110 Ϯ 9 vs. 197 Ϯ 32 mol/g dry wt, P Ͻ 0.05). Analysis of plasma glucose 2 H enrichments at the end of the feeding period also revealed a significantly higher fractional contribution of triose phosphate to plasma glucose levels in HS vs. SC. Hence, the 2 H enrichment distributions of hepatic glycogen and glucose from 2 H2O inform the contribution of dietary fructose to hepatic glycogen and glucose synthesis. deuterated water; direct and indirect pathways; fructose; hepatic glycogen; sucrose DIETARY FRUCTOSE CAN SIGNIFICANTLY BENEFIT (20, 21) or substantially hinder (7, 10, 30) glycemic control, depending on the quantity consumed, and these contrasting effects are reflected by alterations in postprandial hepatic glycogen synthesis. Low levels of dietary fructose activate glucokinase, thereby promoting direct pathway conversion of glucose into glycogen and enhancing net hepatic glucose uptake (19). In contrast, high fructose intake is characterized by its unregulated conversion into triose phosphates (triose-P) that in turn promote excessive gluconeogenic and lipogenic fluxes (5, 30). In the postprandial state, triose-P fluxes can also support high indirect pathway fluxes of glycogen synthesis competing with glycogenesis from glucose, thereby reducing net hepatic glucose uptake. Therefore, the contributions of dietary fructose and glucose to hepatic glycogen synthesis fluxes inform the distinction between catalytic levels of dietary fructose that are benefic...

The Sweet Path to Metabolic Demise: Fructose and Lipid Synthesis

“…A recent study assessing the pathways of glycogen synthesis in sucrose fed rats compared to regular chow fed rats found ~ 4-fold increase in the contribution of triose phosphates to glycogen synthesis which reflects the contribution of fructose [18]. Fructose, or specifically F1P, activates glucokinase (Gck), by promoting the release of Gck from Glucokinase Regulatory Protein (Gckr) in the nucleus [19, 20].…”

Disposition of [U-2H7]glucose into hepatic glycogen in rat and in seabass

“…The analysis of hepatic glycogen synthesis with labeled water is a versatile approach that provides information about the fractional replacement of glycogen during feeding as well as informing the substrates that contribute to glycogen synthesis (Postle and Bloxham, 1980;Jones et al, 2006b;Soares et al, 2012;Viegas et al, 2012;Delgado et al, 2013). The analysis relies on certain assumptions concerning exchange of hydrogens between sugar phosphates and body water.…”

Metabolic incorporation of H218O into specific glucose‐6‐phosphate oxygens by red‐blood‐cell lysates as observed by 13C isotope‐shifted NMR signals

“…sources of glucose and glycogen synthesis since it is incorporated into specific sites of glucose-6-phosphate via specific enzyme-mediated exchange/addition mechanisms. Unlike 2 H, 18 O does not experience significant isotope effects for any of these processes. Therefore, H 2 18 O might provide more precise estimates of endogenous carbohydrate synthesis compared with deuterated water provided that positional 18 O enrichments of glucose can be measured.…”