The Inflammation Biomarker GlycA Reflects Plasma N-Glycan Branching

Abstract

Background: GlycA is a nuclear magnetic resonance (NMR) signal in plasma that correlates with inflammation and cardiovascular outcomes in large data sets. The signal is thought to originate from N-acetylglucosamine (GlcNAc) residues of branched plasma N-glycans, though direct experimental evidence is limited. Trace element concentrations affect plasma glycosylation patterns and may thereby also influence GlycA.

Methods: NMR GlycA signal was measured in plasma samples from 87 individuals and correlated with MALDI-MS N-glycomics and trace element analysis. We further evaluated the genetic association with GlycA at rs13107325, a single nucleotide polymorphism resulting in a missense variant within SLC39A8, a manganese transporter that influences N-glycan branching, both in our samples and existing genome-wide association studies data from 22 835 participants in the Women's Health Study (WHS).

Results: GlycA signal was correlated with both N-glycan branching (r2 ranging from 0.125-0.265; all P < 0.001) and copper concentration (r2 = 0.348, P < 0.0001). In addition, GlycA levels were associated with rs13107325 genotype in the WHS (β [standard error of the mean] = -4.66 [1.2674], P = 0.0002).

Conclusions: These results provide the first direct experimental evidence linking the GlycA NMR signal to N-glycan branching commonly associated with acute phase reactive proteins involved in inflammation.

Fig. 1.

GlycA signal associates with N-glycan branching. The relative abundance of mono- (A), bi- (B), tri- (C), and tetra- (D) antennary N-glycans measured by MALDI-TOF mass spectrometry from 87 human plasma were analyzed using linear regression against GlycA level detected by ¹H NMR. GlycA level showed a significant negative correlation with the abundance of biantennary glycans and a significant positive correlation with tri- and tetra-antennary glycans. Individual data points are shown with line of best fit (solid) and its 95% confidence intervals (dotted). GlycA concentration is expressed in µmol/L.

Fig. 2.

GlycA signal associates with Cu but not other metals involved in glycosylation. Correlations between GlycA signal and the concentration of Mn (A), Co (B), Cu (C), and Zn (D). Individual data points are shown with line of best fit (solid) and its 95% confidence intervals (dotted). GlycA concentration is expressed in µmol/L.

Fig. 3.

rs13107325 genotype associates with GlycA level in the WHS dataset. (A), GlycA levels stratified by rs13107325 genotype from samples analyzed for N-glycomics and metal concentrations in the MGB Biobank. GlycA mean levels in minor allele carriers are reduced but fall short of significance. Data presented as a violin plot with median ± interquartile ranges. Total sample size = 107; CC = 42; CT = 41; TT = 24; (B), GlycA levels from the WHS stratified by rs13107325 genotype. The minor allele results in a small but significant effect on GlycA levels on a population level. Data presented as a violin plot with median ± interquartile ranges. Total sample size = 22 835 participants; imputed genotypes CC = 19 880, CT = 2850, and TT = 105.