Meteorin-like Protein (Metrnl) and Coronary Collateral Circulation in Patients with Chronic Total Occlusion: A Prospective Observational Study

Background Coronary collateral circulation (CCC) mitigates ischemia, preserves myocardial viability, and improves outcomes in patients with advanced coronary artery disease. However, molecular determinants of inter-individual variability in CCC remain poorly defined. Meteorin-like protein (Metrnl) is a novel adipomyokine with cardioprotective, metabolic, and immunoregulatory properties, but its relationship with CCC has not been clarified. Objectives To evaluate the association between serum Metrnl levels and CCC in patients with chronic coronary syndrome and chronic total occlusion, and to investigate the relationship between Metrnl and angiographic severity scores. Methods This prospective, single-center study included 98 patients with chronic coronary syndrome and at least one chronic total occlusion in a major epicardial coronary artery. CCC was assessed angiographically using the Rentrop classification. Patients were stratified into poor CCC (Rentrop 0–1, n = 33) and good CCC (Rentrop 2–3, n = 65) groups. Baseline clinical characteristics, medications, biochemical and hematological parameters, inflammatory indices, and angiographic findings were recorded. Serum Metrnl levels were measured using a standardized ELISA. Coronary disease severity was quantified with SYNTAX II and Gensini scores. Results Clinical features, prior medication use, lipid profile, and most inflammatory markers did not differ significantly between poor and good CCC groups. Serum Metrnl levels were comparable in poor versus good CCC (1.73 ± 0.15 vs. 1.67 ± 0.16 ng/mL, p = 0.093), and Metrnl did not correlate with body mass index, lipid parameters, or high-sensitivity C-reactive protein. In contrast, Metrnl levels were inversely associated with angiographic severity: Gensini score (r = − 0.360, p < 0.001) and SYNTAX score (r = − 0.372, p < 0.001). ROC analysis showed no discriminatory value of Metrnl for distinguishing poor from good CCC (AUC 0.520, p = 0.789). In univariate logistic regression, higher SYNTAX score was significantly associated with good CCC (odds ratio 1.069; 95% confidence interval 1.004–1.138; p = 0.038). Conclusions In patients with chronic coronary syndrome and chronic total occlusion, serum Metrnl levels are not linked to the extent of CCC but are inversely correlated with coronary atherosclerotic burden as reflected by SYNTAX and Gensini scores. Metrnl may represent a biomarker of disease severity rather than collateralization.