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Deuterated water ( 2 H 2 O) is widely used for measuring de novo lipogenesis (DNL). 2 H is incorporated into fatty acids via exchange between body water and the hydrogens of acetyl-CoA, malonyl-CoA, and NADPH. Previous studies concluded that these exchanges are incomplete; therefore, fatty acid 2 H enrichment requires correcting. In mice, we measured the 2 H enrichment of fatty acid positions 2 and 3 and methyl hydrogens from [U- 2 H 7 ]glucose to determine 2 H transfer from glucose to fatty acid via malonyl-CoA, NADPH, and acetyl-CoA, respectively. Positional fatty acid 2 H enrichments were compared with 13 C enrichment of the same sites from an equivalent amount of [U- 13 C 6 ]glucose provided alongside the [U- 2 H 7 ]glucose tracer. Transfer of glucose 2 H to fatty acid position 2 and methyl sites was low ( 2 H enrichment of 0.06 ± 0.01 and 0.14 ± 0.01 relative to 13 C) indicating extensive exchange at both malonyl- and acetyl-CoA, respectively. Transfer of glucose 2 H into fatty acid position 3 was more extensive (0.46 ± 0.04 relative to 13 C, P < 10 -5 vs. position 2), indicating a more limited exchange of those glucose hydrogens that were transferred via NADPH. However, mice provided with [U- 13 C 6 ]glucose and 2 H 2 O had equivalent 2 H enrichments of fatty acid positions 2 and 3, suggesting that in this setting, NADPH and body water 2 H had exchanged extensively. This is explained by contributions of substrates other than exogenous glucose to DNL coupled with their extensive 2 H enrichment from 2 H 2 O prior to DNL. Under such conditions, 2 H enrichment of fatty acids from 2 H 2 O does not need correction., (Copyright © 2019 Belew et al.)

Farmed seabass have higher adiposity than their wild counterparts and this is often attributed to carbohydrate (CHO) feeding. Whether this reflects a reduction in fat oxidation, increased de novo lipogenesis (DNL), or both, is not known. To study the effects of high CHO diets on hepatic TG biosynthesis, hepatic TG deuterium ((2)H) enrichment was determined following 6 days in (2)H-enriched tank water for fish fed with a no-CHO control diet (CTRL), and diets with digestible starch (DS) and raw starch (RS). Hepatic fractional synthetic rates (FSRs, percent per day(-1)) were calculated for hepatic TG-glyceryl and FA moieties through (2)H NMR analysis. Glyceryl FSRs exceeded FA FSRs in all cases, indicating active cycling. DS fish did not show increased lipogenic potential compared to CTRL. RS fish had lower glyceryl FSRs compared with the other diets and negligible levels of FA FSRs despite similar hepatic TG levels to CTRL. DS-fed fish showed higher activity for enzymes that can provide NADPH for lipogenesis, relative to CTRL in the case of glucose-6-phosphate dehydrogenase (G6PDH) and relative to RS for both G6PDH and 6-phosphogluconate dehydrogenase. This approach indicated that elevated hepatic adiposity from DS feeding was not attributable to increased DNL., (Copyright © 2016 by the American Society for Biochemistry and Molecular Biology, Inc.)