Effects of Empagliflozin Treatment on Glycerol-Derived Hepatic Gluconeogenesis in Adults with Obesity: A Randomized Clinical Trial

Abstract

Objective: The aim of this study was to determine the effects of empagliflozin on glycerol-derived hepatic gluconeogenesis in adults with obesity without type 2 diabetes mellitus (T2DM) using oral carbon 13 (13 C)-labeled glycerol.

Methods: A randomized, double-blind, placebo-controlled trial was performed in participants with magnetic resonance imaging assessment of body fat and measurement of glycerol-derived 13 C enrichment in plasma glucose by nuclear magnetic resonance spectroscopy following ingestion of [U-13 C3 ]glycerol. Participants were randomized to oral empagliflozin 10 mg once daily or placebo for 3 months. Glycerol-derived 13 C enrichment studies were repeated, and treatment differences in the mean percentage of 13 C glycerol enrichment in glucose were compared using mixed linear models.

Results: Thirty-five participants completed the study. Empagliflozin increased glycerol-derived 13 C enrichment between baseline and follow-up by 6.5% (P = 0.005), consistent with less glycerol from visceral adipose tissue (VAT). No difference was found with placebo. Glycerol-derived 13 C enrichment was lower in participants with high VAT compared with low VAT by 12.6% (P = 0.04), but there was no heterogeneity of the treatment effect by baseline VAT. Glycerol-derived 13 C enrichment was inversely correlated with VAT but was not correlated with weight loss.

Conclusions: VAT is associated with endogenous glycerol-derived hepatic gluconeogenesis, and empagliflozin reduces endogenous glycerol gluconeogenesis in adults with obesity without T2DM. These findings suggest a mechanism by which sodium-glucose cotransporter 2 inhibitors may prevent T2DM in obesity.

Trial registration: ClinicalTrials.gov NCT02833415.

Conflict of interest statement

Relationship with Industry/Conflict of Interest: Dr. Neeland has previously received honoraria, consulting, and speaker’s bureau fees, and travel support from Boehringer-Ingelheim/Lilly Alliance, a research grant from Novo Nordisk, and has been a member of the scientific advisory board of AMRA Medical. All other authors have no relationship with industry/conflicts of interest to report.

© 2020 The Obesity Society.

Figures

Figure 1.. CONSORT Study selection diagram.

Healthy obese adults without type 2 diabetes were screened for eligibility in the trial and 40 were randomized to empagliflozin/matching placebo. Four participants did not return for follow-up procedures and 1 participant was excluded immediately after randomization due to diagnosis of type 2 diabetes. 35 participants (18 empagliflozin/17 matching placebo) had full data available for the modified intention-to-treat analysis.

Figure 2.. Effects of empagliflozin treatment on weight, glycosylated hemoglobin, systolic blood pressure, and glucagon.

Empagliflozin significantly reduced hemoglobin A1c and systolic blood pressure with a non-significant trend toward greater body weight loss. There was no significant treatment-effect on plasma glucagon levels.

Figure 3.. Effects of empagliflozin treatment on excess 13C enrichment in glucose.

Contribution of [U-13C3] glycerol to glucose production via hepatic gluconeogenesis in participants treated with empagliflozin (top panel) and matching placebo (bottom panel). There was a statistically significant 6.5% increase in the area under the curve for 13C enrichment in glucose in the empagliflozin treated group and no treatment difference with placebo. Baseline to follow-up comparisons were made using mixed linear models to account for all time points at each visit.

Figure 4.. Excess 13C enrichment in glucose stratified by visceral adipose tissue level.

Contribution of [U-13C3] glycerol to glucose production via hepatic gluconeogenesis in participants with high VAT (squares) and low VAT (circles) at baseline. There was a statistically significant 12.6% lower area under the curve for 13C enrichment in glucose in the high VAT group compared to low VAT group. High/low defined as > or ≤ the sex-specific median population value. VAT=visceral adipose tissue.

Figure 5.. Change in peak 13C enrichment in glucose by change in body weight.

Change in body weight (lbs) was not significantly correlated with change in peak 13C enrichment in blood glucose (Spearman ρ= −0.12, p=0.49).

Figure 6.. Hypothesized effect of empagliflozin on glycerol-derived hepatic gluconeogenesis.

Glycerol-gluconeogenesis is directly interrogated by determining the fraction of 13C3 enrichment in blood glucose using NMR spectroscopic quantification of 13C–labeled glucose isotopomers. Total 13C enrichment in plasma glucose is measured by the sum of all glucose isotopomers with excess 13C. Empagliflozin treatment may decrease visceral adipose tissue thereby reducing its contribution of cold (endogenous) glycerol and/or cold PEPCK-derived substrates into this pathway (red hashed flat arrow). Additional information about specific pathways is derived from specific glucose isotopomers. Initially, glycerol is phosphorylated in the liver by glycerol kinase and is converted to DHAP and GA3P. Direct production of glucose via gluconeogenesis occurs by condensation of DHAP and GA3P to form carbons 1–3 and 4–6 of glucose, respectively. Therefore, quantification of [1,2,3-13C3] glucose and of [4,5,6-13C3] glucose reflects primarily direct hepatic gluconeogenesis from ingested [U-13C3] glycerol (black filled circles). Passage of [1,2,3-13C3] G6P through the PPP produces [1,2-13C2] F6P and subsequently [1,2-13C2] glucose so that the quantification of [1,2-13C2] glucose reflects PPP activity (red filled circles). Metabolism of [U-13C3] glycerol to [U-13C3] pyruvate followed by either decarboxylation to [U-13C2] acetyl-CoA or carboxylation to [1,2,3-13C3] oxaloacetate allows rearrangement of 13C in the TCA cycle to form PEP. Two possible PEP isotopomers through glycerol metabolism in the TCA cycle are [1,2-13C2]- and [2,3-13C2] PEP. Conversion to PEP and metabolism to glucose will produce [4,5-13C2]- or [5,6-13C2] glucose (green filled circles). Since the PPP does not disrupt carbon–carbon bonds in carbons 4–6 of glucose, the presence of [4,5-13C2]- or [5,6-13C2] glucose indicates metabolism of [U-13C3] glycerol through the TCA cycle prior to gluconeogenesis. DHAP = dihydroxyacetone phosphate; GA3P = glyceraldehyde 3-phosphate; G6P = glucose 6-phosphate; F6P = fructose 6-phosphate; NMR = nuclear magnetic resonance; PEP = phosphoenolpyruvate; PEPCK = PEP carboxykinase; PPP = pentose phosphate pathway, TCA = tricarboxylic acid; TPI = triose phosphate isomerase.