OBJECTIVE: Atrial fibrillation (AF) is the most common arrhythmia and is associated with an increased risk of stroke. However, the molecular mechanisms leading to AF still remain largely unknown. Novel ‘omics’ approaches can help to unravel the complexity of the disease, investigating the whole transcriptome, proteome and metabolome, and importantly the interconnection between these molecular levels. The aim of this project is to use metabolomics to identify and analyze novel associations between metabolites and AF.

METHODS: Metabolomic profiles were generated by high-throughput liquid chromatography–mass spectrometry (LC-MS) using the Absolute IDQ p180 kit (Biocrates). Screening was performed in serum samples of a case-cohort including 632 AF cases and 9028 non-cases within the European BiomarCaRE project. Multivariate Cox proportional hazards models were used to assess the associations between metabolites and AF. Replication of significant metabolites was performed in serum and tissue samples of 118 AF cases and controls from the Atrial Fibrillation Clinical Cohorts study (AF_CCS) of the University Heart Center Hamburg.

To investigate an effect of the identified metabolites on cardiac function, we stimulated ventricular rat engineered heart tissue (EHT) with different concentrations of the identified metabolite (1 µM, 5 µM, 25 µM, average human plasma concentration in BiomarCaRE 0,1 µM) for one week (n = 9 per group).

RESULTS: Using a screening and replication approach, the mono-unsaturated long-chain acylcarnitine C18:1 (in its non-hydroxylated and hydroxylated form) was identified as a plasma metabolite significantly associated with a higher risk of AF (hazard ratio = 1.61; P-Value = 0.007).

During treatment of ventricular rat EHTs, the highest concentration of C18:1 induced an impairment of contractility after one day of stimulation. Additionally, we observed a time-dependent effect of the lower concentrations on contractile force (mean differences 0.03 mN, P-value < 0.05) after one week, arguing for a pro-arrhythmic effect of C18:1 rather than an association only. To account for the differences between atrial and ventricular cardiomyocytes, we have now established a novel atrial EHT model which we will use in the same way to gain further insight into the association of C18:1 with AF.

CONCLUSION: By metabolomics profiling, we identified a novel association between plasma long-chain acylcarnitine C18:1 and AF. In preliminary in vitro experiments a potential detrimental effect of this acylcarnitine on contractility was observed indicating a contribution of the acylcarnitine to the pathophysiology of AF. Further investigation of the metabolite might not only lead to new insights into the pathomechanisms of AF but C18:1 might also represent a novel biomarker for AF.