GlycA measured by NMR spectroscopy is associated with disease activity and cardiovascular disease risk in chronic inflammatory diseases☆

GlycA is a biomarker of systemic inflammation, quantifying both the protein concentrations and glycosylation states of several acute phase proteins. GlycA has been shown to be associated with both subclinical atherosclerosis and with cardiovascular disease (CVD). GlycA levels are higher in acute and chronic inflammation. During ongoing systemic inflammatory processes, GlycA specific acute phase reactants and proteins undergo circulating concentration and glycosylation pattern changes, and these alterations are reflected in the GlycA NMR signal. Additionally, levels associate with ongoing disease severity in individuals with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and psoriasis thus capturing active inflammation. Furthermore, in these disease states, GlycA is associated with cardiovascular disease (CVD) independent of traditional risk factors including C-reactive protein (CRP). Finally, GlycA levels decrease with exercise, weight loss, and systemic anti-inflammatory agents. Therefore, GlycA appears to be a promising new composite biomarker of active systemic inflammation including assessing CVD risk in patients with inflammatory diseases.


Introduction
GlycA is a biomarker of systemic inflammation, quantifying both the protein concentrations and glycosylation states of several acute phase proteins (Fig. 1). GlycA has been shown to be associated with both subclinical atherosclerosis and with cardiovascular disease (CVD). GlycA levels are higher in acute and chronic inflammation whereby GlycAspecific acute phase reactants and proteins undergo circulating concentration and glycosylation pattern changes. These alterations are reflected in the GlycA NMR signal readily measurable with routine lab assessment. In this review, we will cover how GlycA levels associate with ongoing disease severity in individuals with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and psoriasis as well as various forms of CVD in those with or without chronic inflammation.
These recommendations have been incorporated into guidelines from the AHA/ACC as well as the AAD/EULAR for both RA, SLE, and, more recently, psoriasis management [20,21]. However, addressing CVD risk in chronic inflammation is complicated. In RA, CVD risk assessment and traditional lipid panels-such as low density lipoprotein cholesterol (LDL-C) are not good predictors of CVD risk [12,13,17,22,23]. The presence of seemingly normal or low LDL-C and HDL-C despite greater CVD risk is referred to as the "lipid paradox" [17,[22][23][24][25]. Furthermore, recent evidence has also demonstrated that inflammatory markers such as high sensitivity C-reactive protein (hsCRP)-may not accurately predict cardiovascular disease risk in inflammatory disease states such as systemic lupus erythematosus [26], psoriasis [27], and rheumatoid arthritis [28]. The lipid paradox and additional effects of masked inflammation reduce the accuracy of typical CVD risk estimators when used in chronic inflammatory diseases. This is important to address since the interaction between systemic inflammation and lipoprotein leads to smaller, atherogenic LDL particles with reduced high density lipoprotein (HDL)-C accelerating inflammation-associated atherosclerosis [12,17,[22][23][24][25]. While hsCRP is a reliable predictor of prospective cardiovascular risk in the general population, in patients with RA, adding hsCRP to the Framingham Risk Score and QRISK2 equations did not improve reclassification [12,14,29]. Furthermore, GlycA, and not hsCRP, provided additional value beyond traditional risk factors in association with subclinical CVD in psoriasis patients (30). Therefore, to adequately assess CVD risk in patients with chronic inflammatory diseases, new diagnostic tests that capture the residual CVD risk are needed. GlycA may represent one of these new diagnostic tests that one can leverage to detect ongoing active inflammation in high-risk states; moreover it is now available for physician use.

GlycA is a biomarker of systemic inflammation and CVD risk
As an alternative to traditional inflammatory markers, contemporary biomarkers of systemic inflammation including nuclear magnetic resonance (NMR)-measured GlycA, have been explored. GlycA quantifies systemic inflammation by assessment of an array of acute phase proteins [31][32][33][34]. During ongoing systemic inflammatory processes, these proteins undergo circulating concentration and glycosylation pattern changes, and these alterations are reflected in the GlycA NMR signal [31][32][33][34]. Theoretically, the GlycA NMR signal arises from all circulating glycosylated proteins in the liver. The proteins circulating at high enough concentrations to make significant contributions to the GlycA signal are the late acute phase reactants α1-acid glycoprotein, haptoglobin, α1-antitrypsin, α1-antichymotrypsin, and transferrin. Moreover, two of the major protein contributors to the GlycA signal, α1-acid glycoprotein and haptoglobin, are synthesized in and secreted from neutrophil granules, suggesting that, besides the liver, neutrophils may be a relevant source of elevated GlycA [31][32][33][34].
GlycA concentrations are greater with both acute illnesses [35] and chronic inflammatory diseases and may be a better reflection of a systemic acute phase response than any single glycoprotein component since it is a composite marker stable over time and thus, has lower intra-individual variability [30,32,[36][37][38][39][40]. In addition to high levels of systemic inflammation, GlycA concentrations correlate with the indolent inflammation present in cardiometabolic risk factors, obesity, insulin resistance, and the metabolic syndrome [33,39]. Thus, in chronic inflammatory diseases with low grade persistent inflammation, GlycA may serve as a biomarker of both systemic disease activity as well as cardiometabolic risk [30,32,[36][37][38][39][40].
GlycA concentrations are associated with both prevalent and incident CVD events independent of traditional risk factors [32] (Table 1). GlycA is associated with the presence and extent of coronary artery disease (CAD) and peripheral artery disease (PAD) [41][42][43], and in persons with clinical and subclinical CVD [44,45]. Independent of traditional CVD risk factors and clinical parameters, GlycA concentrations are associated with incident CVD events, as noted in the Women's Health Study (WHS) [46], the Prevention of Renal and Vascular End-stage Disease (PREVEND) Study [47], the Multi-Ethnic Study of Atherosclerosis (MESA) [48], the Intermountain Health Collaborative Study [49], the Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Outcomes (AIM-HIGH) trial [50], the Dallas Heart Study [51], and the Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER) [52]. Moreover, multiple studies including the CATHGEN (CATHeterization GENetics) cardiac catheterization biorepository have demonstrated that GlycA is associated with not only presence or extent of coronary artery disease and cardiovascular mortality but also with all-cause mortality and non-cardiovascular mortality even when accounted for traditional cardiovascular risk factors. Notably, these prospective associations are only modestly attenuated-if at all-by hsCRP, implying that GlycA and hsCRP may denote different components of chronic inflammatory processes.

GlycA is a marker of disease activity and CVD risk in patients with chronic inflammatory disease
GlycA is associated with both disease activity and CVD in patients with RA, SLE and psoriasis [32] and captures active and ongoing systemic    inflammation ( Table 2). In RA, GlycA levels are increased and strongly associated with disease activity by RA severity scores. Furthermore, GlycA was associated with coronary calcium scores [36,39]. Additionally, in SLE, GlycA concentrations are higher, increase with disease activity as assessed by the SLEDAI, and associate with non-calcified coronary artery plaque burden by coronary CTA in SLE patients [37,38,53]. In psoriasis, GlycA concentrations are also elevated, strongly associated with cutaneous disease severity by PASI scores and associated with subclinical vascular diseases assessed by FDG PET/CT aortic vascular inflammation and CTA derived coronary artery disease burden [30]. Interestingly, in that study, GlycA concentrations captured sub-clinical vascular disease incrementally over hsCRP, and also decreased when skin disease was treated suggesting it tracked disease activity [30]. Thus, GlycA may be an effective clinical tool for assessing both disease activity and CVD risk in patients with chronic inflammatory diseases, even when patients are on treatment with anti-inflammatory therapies [36,54].

GlycA levels change in response to exercise, weight loss, and antiinflammatory agents
Circulating GlycA levels are favorably modified by lifestyle changes such as exercise in the absence of dietary modifications [55][56][57]. Exercise training reduces GlycA independent of age, sex, race, baseline body mass index and beyond baseline GlycA levels, and occurred with 14 different interventions and seven distinct populations [56]. In addition to exercise training, GlycA is favorably modified by bariatric surgery with concomitant weight loss suggesting a tight association with body fat [58]. In persons with RA and psoriasis, GlycA concentrations are reduced with anti-inflammatory treatments using inhibitors of JAK1/2, TNFα, IL-17A or IL-12/IL-23 [30,[59][60][61][62], whereas GlycA concentrations are largely unaffected by treatment with a statin or extended release niacin [50,52]. Thus, in persons with chronic inflammatory diseases, GlycA may be useful clinically for monitoring disease activity and/or CVD risk reductions following both pharmacologic and lifestyle interventions.

Clinical perspective
GlycA can be measured in the general population as an additional marker of CVD risk for primary or secondary prevention. GlycA is strongly associated with CVD risk in patients with chronic inflammatory illnesses, even beyond hsCRP. Moreover, a value of 400 μmol/L has been accepted as the cut-point for systemic inflammatory states. In this population, those who have higher values have been shown to have more CVD risk. As for the general population, we would expect the cut-point to be lower when it comes to risk stratification regarding secondary prevention, however studies focusing on concrete cut-points are lacking.
Given the available data, it appears that GlycA levels less than 400 μmol/ L are relate to low CVD risk in chronic inflammation in those without overt clinical CVD. Levels greater than or equal to 400 μmol/L are indicative of greater inflammation-related CVD risk. Potentially, GlycA could serve to provide CV stratification in patients with RA, PSO and SLE when the value is beyond 400. GlycA levels above 400 μmol/L may trigger more aggressive measures for treatment of CV risk factors, recommendation of physical activity, weight loss, and perhaps more aggressive treatment of the underlying inflammatory disease. Early observational studies have shown promise of GlycA association with CV risk in inflammatory states beyond hsCRP, and support the conduct of prospective, randomized studies using GlycA to identify patients at highrisk for CVD [30][31][32][33][34].

Conclusions
Traditional assessments of CVD risk including lipid panel assessment, Framingham risk score, and hsCRP do not effectively capture the higher risk of CVD in chronic inflammatory diseases. Prediction of the CVD risk in these diseases may be improved with measurement of GlycA, a composite measure of concentrations and glycosylation of acute phase proteins. In chronic inflammatory diseases, GlycA concentrations associate with both traditional CVD risk factors as well as disease activity. GlycA concentrations respond to nonpharmacologic interventions targeting CVD risk, including exercise and weight loss, as well as pharmacologic agents targeting inflammatory pathways. Thus, in chronic inflammatory diseases, GlycA offers a promising tool to monitor systemic inflammation and CVD risk.

Funding sources
This study was supported by the National Heart, Lung and Blood Institute (NHLBI) Intramural Research Program (HL006193-06). The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclosures
Dr. Mehta is a full-time US government employee and has served as a consultant for Amgen, Eli Lilly, and Leo Pharma receiving grants/other payments; as a principal investigator and/or investigator for AbbVie, Celgene, Janssen Pharmaceuticals, Inc, and Novartis receiving grants and/or research funding; and as a principal investigator for the National Institute of Health receiving grants and/or research funding.

Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.