Transfer of glucose hydrogens via acetyl-CoA, malonyl-CoA, and NADPH to fatty acids during de novo lipogenesis

Abstract

Deuterated water (²H₂O) is widely used for measuring de novo lipogenesis (DNL). ²H 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 ²H enrichment requires correcting. In mice, we measured the ²H enrichment of fatty acid positions 2 and 3 and methyl hydrogens from [U-²H₇]glucose to determine ²H transfer from glucose to fatty acid via malonyl-CoA, NADPH, and acetyl-CoA, respectively. Positional fatty acid ²H enrichments were compared with ¹³C enrichment of the same sites from an equivalent amount of [U-¹³C₆]glucose provided alongside the [U-²H₇]glucose tracer. Transfer of glucose ²H to fatty acid position 2 and methyl sites was low (²H enrichment of 0.06 ± 0.01 and 0.14 ± 0.01 relative to ¹³C) indicating extensive exchange at both malonyl- and acetyl-CoA, respectively. Transfer of glucose ²H into fatty acid position 3 was more extensive (0.46 ± 0.04 relative to ¹³C, 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-¹³C₆]glucose and ²H₂O had equivalent ²H enrichments of fatty acid positions 2 and 3, suggesting that in this setting, NADPH and body water ²H had exchanged extensively. This is explained by contributions of substrates other than exogenous glucose to DNL coupled with their extensive ²H enrichment from ²H₂O prior to DNL. Under such conditions, ²H enrichment of fatty acids from ²H₂O does not need correction.

Keywords: acetyl-coenzyme A; deuterium nuclear magnetic resonance; malonyl-coenzyme A; pentose phosphate pathway; reduced nicotinamide adenine dinucleotide phosphate.