Circulating total and H-specific GDF15 levels are elevated in subjects with MASLD but not in hyperlipidemic but otherwise metabolically healthy subjects with obesity

Abstract

Background: Growth differentiation factor 15 (GDF15) is a mitokine, the role of which, total or H-specific, in modulating energy metabolism and homeostasis in obesity-related diseases, such as metabolic dysfunction associated steatotic liver disease (MASLD), has not been fully elucidated in adult humans. We aimed to investigate the fasting and stimulated levels of GDF15, total and H-specific, glucose-dependent insulinotropic polypeptide (GIP) and C-peptide, in two physiology interventional studies: one focusing on obesity, and the other on MASLD.

Methods: Study 1 investigated individuals with normal weight or with obesity, undergoing a 3-h mixed meal test (MMT); and study 2, examined adults with MASLD and controls undergoing a 120-min oral glucose tolerance test (OGTT). Exploratory correlations of total and H-specific GDF15 with clinical, hormonal and metabolomic/lipidomic parameters were also performed.

Results: In study 1, 15 individuals were included per weight group. Fasting and postprandial total and H-specific GDF15 were similar between groups, whereas GIP was markedly higher in leaner individuals and was upregulated following a MMT. Baseline and postprandial C-peptide were markedly elevated in people with obesity compared with lean subjects. GIP was higher in leaner individuals and was upregulated after a MMT, while C-peptide and its overall AUC after a MMT was markedly elevated in people with obesity compared with lean subjects. In study 2, 27 individuals were evaluated. Fasting total GDF15 was similar, but postprandial total GDF15 levels were significantly higher in MASLD patients compared to controls. GIP and C-peptide remained unaffected. The postprandial course of GDF15 was clustered among those of triglycerides and molecules of the alanine cycle, was robustly elevated under MASLD, and constituted the most notable differentiating molecule between healthy and MASLD status. We also present robust positive correlations of the incremental area under the curve of total and H-specific GDF15 with a plethora of lipid subspecies, which remained significant after adjusting for confounders.

Conclusion: Serum GDF15 levels do not differ in relation to weight status in hyperlipidemic but otherwise metabolically healthy individuals. In contrast, GDF15 levels are significantly increased in MASLD patients at baseline and they remain significantly higher compared to healthy participants during OGTT, pointing to a role for GDF15 as a mitokine with important roles in the pathophysiology and possibly therapeutics of MASLD. Trial registration ClinicalTrials.gov NCT03986684, NCT04430946.

Keywords: C-peptide; GIP; Growth differentiation factor 15; Mixed meal test; Non-alcoholic fatty liver disease; Obesity; Oral glucose tolerance test.

Fig. 1

Fasting levels of total and H-specific GDF15, GIP, and C-peptide and their response to a mixed meal test in Study 1. Bars/points, and error bars reflect means ± SEM. Within bar charts, *, **, *** for the unpaired t-test with Welch’s correction comparing columns. Within line graphs, Time, Group and Time * Group for the fixed effects in the linear mixed effects models; and *, **, *** for the post-hoc LSD tests comparing groups within each respective timepoint

Fig. 2

Fasting levels of total and H-specific GDF15, GIP, and C-peptide and their response to 75 g OGTT in Study 2. Bars/points, and error bars reflect means ± SEM. Within bar charts, *, **, *** for the unpaired t-test with Welch’s correction comparing columns. Within line graphs, Time, Group and Time * Group for the fixed effects in the linear mixed effects models; and *, **, *** for the post-hoc LSD tests comparing groups within each respective timepoint

Fig. 3

Fasting and postprandial metabolipidomic profiles, GDF15, C-peptide and GIP in Study 2. a Hierarchically clustered heatmap of top FDR-corrected metabolite and hormonal variances during the OGTT for both groups. Unsupervised clustering pinpointed 5 distinct clusters which contain functionally related and commonly regulated molecules across healthy and MASLD participants, with distinct time courses elucidated in (b), demonstrating the overall normalized trends of all features (simple lines) and the aggregate average line of each cluster (thicker line). c, d, e Split violin plots of the mixed effects models analysis with factors time (denoting OGTT minutes), group (denoting healthy vs. MASLD) and the time * group interaction, showing only molecules with either significant fixed effect and accompanied by FDR-adjusted corresponding p-values. These molecules also belong to the clusters shown in (a) and (b) and are presented likewise. Within-violin bars represent interquartile ranges, rhombuses means, and error bars standard deviations. Circles represent female and triangles male participants. f PLS-DA of all group-time combinations showcasing a distinct overlay and trend for differentiation between MASLD and healthy, alongside VIP scores of the top significant variables driving this differentiation (g). h and i unsupervised PCA within groups analyses of the circulating metabolipidome during all OGTT timepoints demonstrating vectors of the top 5 significant variables driving OGTT variance across each component, for healthy participants and participants with MASLD, respectively