Objective: Atrial fibrillation (AF) represents the most common sustained arrhythmia. However, the underlying molecular mechanisms still remain largely unknown. Novel ‘omics’ approaches can help to unravel the complexity of the disease. Here, we aimed to identify and functionally characterize the association between circulating metabolites and AF combining epidemiological and molecular approaches.

Methods: Metabolomic profiling was performed by mass spectrometry using the Absolute IDQ p180 kit (Biocrates) in serum samples of a case-cohort including 1,437 incident AF cases 7,591 non-cases without prevalent AF. To further determine an association with prevalent AF, measurements were additionally performed in a diseased cohort with patients undergoing open heart surgery (24 prevalent AF cases and 28 respective controls in sinus rhythm). Multivariate analyses were performed to assess the association between metabolites and AF, adjusting for classical cardiovascular risk factors, study center, and lipid lowering drugs. To investigate the effect of identified metabolites on cardiac function, we evaluated the short-term and long-term effect of different concentrations (between 1 µM and 25 µM) in different in vitro models including primary human atrial tissue and atrial and ventricular engineered heart tissue (EHT) generated from human induced pluripotent stem cells.

Results: The circulating  metabolite unsaturated long-chain acylcarnitine C18:1 (AC) was identified as significantly associated with a higher risk of AF (HR = 1.10; p-value = 0.0004). In the diseased cohort, C18:1 AC was significantly associated with persistent AF (FDR < 0.05). Chronic exposure of human atrial and ventricular EHTs to 25 µM C18:1 AC resulted in a progressive impairment of contractility accompanied by a loss of cardiomyocytes and structural disorganization. In addition, human atrial EHT was more susceptible than ventricular EHT and displayed arrhythmia-like contraction behavior. Short-term application resulted in a positive inotropic effect in both EHT models and atrial trabeculae which was reversible, arguing for a specific effect. In addition, the metabolite exposure induced spontaneous contractions in atrial trabeculae representing a surrogate for cardiac arrhythmia.

Conclusion: By a translational approach, the serum long-chain acylcarnitine C18:1 was identified to be associated with the incidence and prevalence of AF in epidemiological cohort studies. The experimental data confirm an arrhythmogenic potential of C18:1 AC which interferes with distinctive mechanisms which are typically affected in AF including contractility, structure, and automaticity of cardiomyocytes. The work underlines the value of ongoing research on metabolomics to evaluate the potential of different disease-associated metabolites for risk prediction, diagnosis or therapeutic interventions in AF.