This study investigated the association of LRG1 and left ventricular diastolic dysfunction (LVDD). We demonstrated that patients with LVDD had significantly higher circulating LRG1 levels compared to patients without LVDD. We found that LRG1 was independently and highly predictive for LVDD. LRG1 could be a suitable marker for the early identification of diastolic dysfunction in at-risk patients as well as for the monitoring of disease progression and treatment effects.
Asymptomatic LVDD increases the risk of adverse cardiovascular events and commonly progresses to symptomatic heart failure with preserved ejection fraction (HFpEF) (10–13). The prevalence of HFpEF is increasing due to an ageing population, increased awareness, refined diagnostic criteria and advances in imaging (14, 15). In fact, symptomatic patients with echocardiographic evidence of diastolic dysfunction, previously subsumed as having “diastolic heart failure” are now being classified as having HFpEF. It is a major public health issue as it accounts for more than half of the total heart failure prevalence (14). Despite its clinical importance, there is no reference strategy for the diagnosis of HFpEF; even more challenging is the identification of asymptomatic patients with LVDD (16). Echocardiographic parameters at early stages of HFpEF are commonly normal at rest and natriuretic peptides are frequently within normal range or only minimally raised (17, 18). Diagnosis at an asymptomatic stage could identify patients that would benefit from early intervention with lifestyle modifications, intensification of treatment regimes, and closer follow-up. Hence, there is an urgent need for a more sensitive marker of diastolic dysfunction.
It has been postulated, that the plethora of comorbidities that is commonly present in HFpEF patients create a proinflammatory state resulting in generalized endothelial inflammation. Reduced nitric oxide bioavailability with negative effects on cyclic GMP content, and protein kinase G activity in adjacent myocytes results in fibrosis, diastolic LV stiffness and HF development (19, 20). Likewise, micro- and macrovascular ischemia has been shown to be a major determinant of diastolic dysfunction (21–25). Inflammation plays a key role in the pathogenesis of atherosclerosis, promotes deposition of LDL in the affected vasculature, and formation of atherosclerotic plaques.
The role of LRG1 as a key regulator of vascular disease associated with inflammation is emerging as studies reported an increased expression of LRG1 in such setting (26–30). LRG1 has been shown to be elevated in animal models of retinopathy (31), in patients with coronary artery disease (26), arterial stiffness (32) and most recently, animal models of cardiac fibrosis (33). It has been proposed, that LRG1 is upregulated in cardiac myocytes during fibrotic cardiac remodelling (31, 33, 34). Liu et al. demonstrated recently, that overexpression of LRG1 attenuated cardiac fibrosis and overt heart failure in the myocardium of heart failure animal models (33). As such, elevated levels of LRG1 likely reflect the physiological compensatory response to a fibrotic process. LRG1 exerts its regulatory anti-fibrotic effect by inhibiting the inflammatory signalling of the transforming growth factor (TGF)-β1 within a complex molecular network involving PPAR (peroxisome proliferator-activated receptor) β/δ, and SMRT (silencing mediator for retinoid and thyroid hormone receptor) (35, 36).
The SYNTAX score is a scoring algorithm that quantifies the extent of coronary atherosclerosis. It is widely used to risk stratify patients in clinical practise and to support decision making (9). We utilised the SYNTAX score as a surrogate marker of the atherosclerotic burden in our study cohort. Pairwise comparison demonstrated, in addition to the elevated LRG1 levels, markedly higher SYNTAX scores in the DD group. The association of LRG1 and new-onset atherosclerotic cardiovascular disease has recently been reported in a cohort of the Framingham Heart Study (37). It has been proposed that the elevation of LRG1 occurs at early, preclinical stages (30, 37).
The potential role of LRG1 in heart failure was first reported by Watson et al (38) who studied a heterogeneous group of patients with overt systolic and diastolic heart failure. He found that LRG1 was consistently overexpressed in high BNP serum and identified heart failure patients independent of BNP. Our study confirmed Watson’s experimental findings in a clinical setting by demonstrating a potentially mechanistic relationship between LRG1, diastolic dysfunction and the extent of vascular disease.
The multivariable logistic regression model showed that LRG1 had significant predictability of DD. The overall high diagnostic accuracy of the regression models in our study was confirmed with ROC analysis. The ROC for the adjusted model demonstrated a high accuracy with an AUC = 0.89 (95% CI: 0.82–0.95). The cut-off value of “9” LRG1 had a 78% sensitivity (95% CI: 65.3–87.7) and 72.3% specificity (95% CI: 57.4–84.4) for predicting DD.
Collectively, our results suggest that LRG1 might be a useful, independent predictor of early, subclinical diastolic dysfunction.
The limitation of our study is the relatively small sample size and the cross-sectional study design. Inclusion of patients with ischemic symptoms at hospital presentation may create a selection bias. The current study did not test for other biomarkers such as brain natriuretic peptides (BNPs) and High Sensitivity C-Reactive Protein (hsCRP) (39). Overall, we consider this research preliminary and encourage replication.